Robert Mafeking Haynes was born in Christchurch on 17 May 1900, the son of Emma Rose King Haynes. His mother married Hugh Macfarlane, a labourer, in 1904, and Bob took his stepfather's family name. He was, however, brought up by his grandmother, Mary Haynes, an unregistered nurse. Bob attended Waltham School and possibly had two years' secondary schooling. He was a keen sportsman: rowing, boxing, cricket and rugby were his favourites. His first job was in a clothing factory, but he claimed later to have been victimised and sacked by his employer; he subsequently worked as a driver for a coal merchant. These experiences contributed to the development of Bob's industrial and political ideals, and he was soon active in both facets of the labour movement.
In his early teenage years he attended socialist meetings with an uncle, and in 1918 joined the Christchurch Socialist Party; soon after he became president. In 1919 he joined the Christchurch South branch of the New Zealand Labour Party, and when the Christchurch East branch was formed in March 1922 he was elected inaugural secretary. Within three years he had become president of the North Canterbury Labour Representation Committee. In the 1927 Labour landslide victory at the Christchurch municipal elections, he was elected to the city council. A keen debater (he had honed his oratorical skills at WEA public-speaking classes), he strove to make an impact in local body politics, but was not re-elected in 1929.
Despite this set-back, Macfarlane continued to agitate in the labour cause. As secretary of several minor unions he was familiar with workers’ concerns as the New Zealand economy deteriorated during the early 1930s. He acted as honorary secretary of the Canterbury Unemployed Workers’ Association and joined the executive of the United Front, an organisation formed to fight cuts to workers’ wages. When a dispute developed among Christchurch union officials over the extent of opposition that should be encouraged, and a leadership tussle ensued, Macfarlane supported the faction aligned to the New Zealand Alliance of Labour rather than the more cautious Canterbury Trades and Labour Council. The conflict between the two groups of officials spilled over into the political arena: in 1931 Macfarlane ousted Bill Green, the longtime secretary of the Trades and Labour Council, from the North Canterbury LRC secretaryship. An astute administrator, he used this position and his union jobs to increase his support.
In 1935, following the death of Elizabeth McCombs, Macfarlane was elected to the Christchurch Tramway Board and the following year he regained his place on the Christchurch City Council. On 17 December 1932 he married Louisa Emily Jacobs at Christchurch. Louisa agreed with her husband's views and became prominent within local bodies herself; she was particularly active on the North Canterbury Hospital Board, serving for 19 years.
In 1938 he was elected mayor of Christchurch on a Labour ticket; the party also secured 10 of the 16 council seats. His victory made him the youngest mayor in the city’s history. He owed his success to the voters in the working-class suburbs of Linwood, Woolston, Spreydon and Sydenham, and later that year he was able to repay them by building pensioner cottages at Sydenham with a subsidy from the first Labour government. Nevertheless, moderate Labour policies were the hallmark of Macfarlane's mayoralty.
In June 1939, at a by-election, Macfarlane was elected Labour MP for Christchurch South. He represented this constituency until 1946 when, after a redrawing of electoral boundaries, he became the member for Christchurch Central, serving until 1969. He was known for his ‘personal attention and assistance to thousands of Christchurch residents’ and for his commitment to local body legislation. When first elected to Parliament the Labour government’s cabinet was well established; Macfarlane never held a ministerial or parliamentary under-secretary position. From 1947 to 1951 he was the party’s senior whip.
Although affiliated with the Socialist Party in his teens, Macfarlane had not opposed military service in the First World War and in 1940 he enlisted in the Second New Zealand Expeditionary Force. Prepared to ‘take on anything and go anywhere’, he did not seek re-election at the 1941 municipal elections. From 1941 to 1943 he served abroad, but, at only five feet seven inches tall and weighing close to 13 stone, the dark-haired, blue-eyed Macfarlane found the heat and physical deprivations of service in the Middle East a trial. Ill health forced his discharge and he returned to Christchurch, where, in 1944, he stood unsuccessfully for the mayoralty. Three years later he was re-elected to the city council and in 1950 he regained the mayoralty. He also served at various times on the Lyttelton Harbour Board and the Christchurch Domains Board.
Although criticised by the Press for being a part-time mayor, he was able to divide his time between parliamentary and mayoral duties when Labour was in opposition during the 1950s. After the second Labour government was elected in 1957, however, he became the Speaker, and the additional commitments in Wellington forced him to resign as mayor in 1958. Bill Rowling maintained later that Macfarlane’s use of ‘common sense rather than the rule book’ assisted the government to survive its full term in office despite a one seat majority. From 1961, with Labour again in opposition, Macfarlane resumed local body service as a city councillor. In 1969 his 30-year parliamentary career ended when he did not seek re-election because of his age; he continued to sit on the city council until his death in Christchurch on 2 December 1981. He was survived by his wife and two daughters. Macfarlane's long years of service to Christchurch and to national politics had been recognised when he was made a CMG in 1954 and knighted in 1974.