Carl August Berendsen was born at Woollahra, New South Wales, on 16 August 1890, the only child of Jurgen Ferdinand Plenge Berendsen, a Swedish immigrant then working as a bank clerk, and his Australian wife, Fannie Asher, the daughter of a Jewish businessman who had been a storekeeper and trader in Wellington in the early 1840s. His mother had, it seems, renounced Judaism, and she raised him as a Christian, though he was never of a religious bent and later confessed to a lifelong 'contempt for the Scriptures'. His father found it difficult to maintain steady employment and was often absent. When Carl was 10 years old he moved with his family to New Zealand. They settled at Waimumu, six miles from Mataura, Southland, where they lived in very straitened circumstances, his father having taken a position as a gold-dredge supervisor. Berendsen later described their house, which was lined with wheat sacks, as a 'monstrosity'.
After a slow start, Berendsen excelled at school. He attended primary school in Mataura, and later Gore District High School, where he was dux in 1905. His academic success led to plans for him to be apprenticed to a cabinetmaker being dropped. He passed the junior civil service examination in December 1905, and began a cadetship in the Department of Education in February 1906. He attended Victoria College part time, graduating LLB in 1914; he was deeply disappointed to gain only second-class honours in his master of laws in 1916. A keen sportsman, he played both rugby and cricket competitively, and represented Wellington in the latter in 1911–12. Berendsen was of medium height, with a dark complexion and a pair of 'almost forbidding eyebrows'.
Following the outbreak of the First World War Berendsen, who had been a member of the Territorial Force for three years and a reluctant officer in a senior cadet company from 1913, volunteered for the expeditionary force which was hastily raised to capture German Samoa. He left with it as a lance corporal on 14 August 1914. After the force was relieved, he was discharged in Wellington in April 1915, and apparently promised his mother that he would not again volunteer for service. Berendsen went back to the Department of Education, remaining with it until May 1916 when he transferred to the Department of Labour. In November of the following year he was promoted to chief clerk, and later became deputy registrar of industrial unions.
By the time of these appointments, Berendsen had been called up for military service, in May 1917. Employed as an instructor at Trentham Military Camp, he was able to continue his courtship of former Education Department colleague Nellie Ellis Brown, whom he married at St John's Church, Wellington, on 15 December 1917; they would have two sons. Berendsen, now a sergeant, did not proceed overseas until October 1918. The war ended before his arrival in Britain in December, at which point he reverted to the rank of corporal. He was at Sling Camp until early in 1919, when he was attached, as a temporary warrant officer, to the high commissioner's office in London for three months to assist with the general election and licensing polls among New Zealand troops. He embarked for home in June 1919.
Berendsen resumed his public service career in August 1919, and immediately won an appeal over his salary. His management style was often abrasive, for he was not averse to swearing and shouting at staff. He spent several months each year visiting district offices throughout New Zealand, and, after being admitted to the Bar in 1924, took many of the department's court cases; he later claimed never to have lost one. However, he did not find the department congenial, and the prospect of eventually becoming its permanent head did not prevent him from readily taking an opportunity in 1926 to transfer to the newly created Prime Minister's Department as imperial affairs officer. Berendsen claimed in his application to have 'intelligence[,] industry, integrity and interest in the proposed position'.
On 21 June 1926 Berendsen took up his new job, the title of which he 'always loathed', with much uncertainty as to what was required of him. He later recalled that departmental head F. D. Thomson 'just took me into my room, told me it was mine, pointed to [a] heap of papers on the table, and said, ‘‘There they are, Berry: they're all yours,’’ and left me to it without another word'. With a staff of two, Berendsen immediately set about preparing for the 1926 Imperial Conference in London, to which he accompanied the prime minister, Gordon Coates.
The imperial affairs officer's role was clarified in March 1927. Berendsen was henceforth responsible for overseeing and co-ordinating all international matters within the purview of the prime minister, and all correspondence with the governor general and the high commissioner in London. He also kept the prime minister in touch with the 'larger aspects' of departmental administration, for which he had regular meetings with permanent heads of the relevant departments.
As political controversy developed in 1927 over New Zealand's administration of its mandate of Western Samoa, Berendsen found himself increasingly involved in advising Coates on Samoan matters. When New Zealand's cruisers were dispatched to Apia in February 1928 in a largely futile effort to back the administration, he went along as Coates's liaison officer. In this 'largely comic opera' situation, his first task was to advise the administrator, Sir George Richardson, of his recall.
Berendsen returned to Wellington in March. His experience had enhanced his value to Coates, who soon formalised his role by appointing him secretary of the Department of External Affairs, the functions of which were chiefly related to Samoa. Berendsen was a member of a committee of inquiry which visited Samoa in November–December 1928 to examine the administration's finances and staff; its report led to severe and far-reaching retrenchment. In 1933 he visited Samoa again. He was also secretary of the departments responsible for the administration of Niue and the Cook Islands.
Berendsen was part of the New Zealand delegation at the 1930 Imperial Conference in London. He then went to Geneva as one of New Zealand's representatives to the League of Nations' Permanent Mandates Commission. On 15 January 1935 he became head of the Prime Minister's Department, a change that 'made no difference whatever' to his duties or functions. In 1936 he was appointed a CMG. Although politically conservative, he sympathised with the Labour government's views on international affairs, especially its emphasis on the League of Nations and the principle of collective security. Berendsen drafted proposals that were submitted, without effect, by New Zealand in 1936 for the reform of the world body. He was also a member of New Zealand's delegation to the league in Geneva that year. He attended the Imperial Conference and the coronation of King George VI in London in 1937, and provided briefing papers for Michael Joseph Savage which criticised appeasement of the fascist dictatorships in Europe. Nevertheless, he was also a realist, and was influential in determining New Zealand strategy after the conference, insisting in 1938 that New Zealand's defence lay in Europe. From September 1937 he was a member of the Council of Defence.
Berendsen oversaw the preparations by the Organisation for National Security for a possible transition to war, and then the implementation of those plans when New Zealand declared war on Germany on 3 September 1939. He accompanied acting Prime Minister Peter Fraser to London for talks about New Zealand's war effort in November 1939, and was involved in discussions on the command of the second New Zealand Expeditionary Force. With the establishment of the War Cabinet in July 1940, he became its secretary. After the overthrow of the pro-Vichy government of Tahiti by Free French supporters in early September 1940, Berendsen went to the island for discussions with the new authorities. The five-day visit culminated with him dancing at a cabaret with 'the ladies of the administration in a scene of great hilarity and enjoyment'. He travelled with Fraser, now prime minister, to the Middle East in 1941, and advised him during his private investigation of the performance of General Freyberg in Greece and Crete.
Berendsen found working with Fraser increasingly uncongenial. Unlike Savage, who had 'treated him with dignity and even deference', Fraser was notoriously insensitive to the feelings of his advisers. Coupled with the heavy workload imposed by the war conditions, and the War Cabinet's unsystematic way of doing business, the clash of personalities had, by early 1943, reduced Berendsen to the verge of a nervous breakdown. The need for a lighter workload led to his appointment in February 1943 as New Zealand's first high commissioner to Australia. The Berendsens were to spend most of the next 10 years outside New Zealand.
Berendsen overcame the teething problems of the new post, and adapted readily to the diplomatic life. Nevertheless, he did not find dealing with the Australian leadership easy, mainly because of differences between the two countries on whether the appropriate place for their contributions to the allied war effort was the Pacific or the Mediterranean. The most important development of his tenure was the signing, mainly at Australian instigation, of the Australia–New Zealand (or Canberra) Agreement on 21 January 1944.
On 16 March 1944 he was appointed, somewhat to his surprise, as New Zealand minister in Washington. After a brief visit to Wellington he took up his post in July. In 1948 the legation was raised to an embassy and Berendsen became ambassador. Although appointed initially for three years, he had his term extended by a year in 1947; this became a yearly ritual until 31 January 1952. In 1949 the incoming National government unanimously agreed to his continuing in office.
In Washington Berendsen, who was made a KCMG in 1946, represented New Zealand at numerous conferences. He sat on the Far Eastern Commission, which somewhat ineffectually oversaw the occupation of Japan, visiting Japan with the commission in 1945 and serving as chairman of the steering committee until 1949. He and Fraser were New Zealand's delegates to the San Francisco Conference in April–June 1945; both signed the United Nations Charter on behalf of New Zealand on 26 June. Disappointed with the outcome, Berendsen was henceforth an implacable opponent of the great-power veto in the Security Council. Between 1946 and 1951 he led the New Zealand delegation at meetings of the General Assembly in New York. Mainly on his own advice, he was appointed New Zealand's permanent delegate at the United Nations on 20 May 1949. From 1947 Berendsen also represented New Zealand on the United Nations Trusteeship Council; he was elected its vice president that year. These duties required him to spend at least eight months each year in New York, and seriously interfered with his ambassadorial duties in Washington.
Although not a natural orator, Berendsen willed himself on to the public stage, always performing flamboyantly and speaking forcefully. A British observer in 1945 noted him making 'the regular sort of demagogic speech which he delights in'. The following year a journalist reported: 'Sir Carl Berendsen, who must play himself when Hollywood gets to filming these debates, breathed fire into the microphone in shouting ‘‘I object and I object with indignation’’ at any aspersion on the good name of New Zealand’.
Berendsen had a good relationship with Alister McIntosh, secretary for external affairs from 1943, and they engaged in a lively correspondence. Younger officials were conscious that he had 'a fearsome reputation for a volcanic temper'. They found him quick to judge, but just as quick to acknowledge error, and he could be intensely loyal to them. McIntosh later described him as 'clear-minded and emphatic – usually dogmatic in his views', with a drafting style that 'reflected this clarity of mind in a style polished and pungent, if not always concise’. Members of his Washington staff later recalled him as 'an extremely decisive man who could not bear shilly-shallying'. He was reputed to have said: 'If you look at a thing and it's 51% black and 49% white then for Christ's sake, it's black’.
As the Cold War developed, Berendsen was quicker than most New Zealand officials to be convinced that the Soviet Union was bent on aggression. He commended the United States’ firm opposition but was upset by questioning of his assumptions by younger officers in the Department of External Affairs when, in early 1948, he made his only visit to Wellington during his Washington service. When Soviet-backed North Korean forces invaded South Korea in June 1950, he applauded the American-inspired United Nations response. After China's intervention in the war, he feared that attempts to negotiate a settlement would lead to the same appeasement that had brought disaster in the late 1930s.
Always mindful of the failure of Commonwealth of Nations defence arrangements in South-east Asia in 1941–42, Berendsen regarded a security commitment by the United States to New Zealand as vitally important. He described the ANZUS treaty, which he signed for New Zealand at San Francisco on 1 September 1951, as 'the greatest gift' that the world's most powerful country could offer to 'a small and comparatively helpless group of people'. One week later, in the same city, he also signed the Japanese Peace Treaty. During the peace conference he gained considerable prominence by moving the tactically important adoption of the rules of procedure – but only after beating the Soviet delegate, Andrei Gromyko, in a dramatic race to the rostrum. Gratified by the warmth of his reception, he described the conference as 'successful beyond my wildest dreams'.
Berendsen became increasingly disillusioned with the government's treatment of him. In 1948 he claimed to have more than 50 grievances 'old and new, dead and alive'. Over-sensitive to slights, he reacted bitterly to what he saw as his mistreatment over appointments to UN delegations, over delays in the upgrading of New Zealand representation in Washington, and, above all, over salary and superannuation. Shortly before his retirement, in January 1952, Berendsen confessed to sadness at closing his service 'with a sense of bitter resentment and indignation at obvious and demonstrable injustices'. He refused to dine with the prime minister on one occasion so angry was he about his treatment.
After Berendsen retired, he and Nellie returned to Wellington, where he characteristically found much to grumble about: too much horse-racing and gambling, overindulgence in alcohol, and 'a menacing dependence of the individual upon the State'. He also resented the fact that he was not asked for advice or comment by the Department of External Affairs, though he occasionally gave it anyway. In September 1952 he set off for North America for the first of a series of annual lecture tours. Typically, for the Berendsens enjoyed travelling to out of the way places, they went by sea via Curaçao. A burst duodenal ulcer nearly killed him on a voyage in 1953. During his retirement he also wrote a voluminous account of his life, which was never published. He died at Dunedin on 12 September 1973, some weeks after suffering a stroke. He was survived by both sons and his wife, who died in 1983.