Alfred Jerome Cadman was born in Sydney, Australia, on 17 June 1847, the son of Jerome Cadman, a cabinet-maker, and his wife, Ann Hildyard. The family came to Auckland, New Zealand, in 1848. Jerome Cadman owned and operated a sawmill in the Coromandel goldfield from 1855 and was later a successful builder and contractor in Auckland. He returned to the Coromandel region in 1867. He served on the abortive Auckland City Council from 1854 to 1855 and on the Auckland Provincial Council, representing Northern Division (1859–67) and Coromandel (1870–76).
Alfred Cadman was educated at the parish schools of St Matthew's and St Paul's, and at Wesley College; he then completed an apprenticeship as a carpenter. He served with the volunteer forces during the wars of the 1860s. At the age of 21 he entered the sawmilling business at Coromandel, and appears to have been very successful as a businessman.
Cadman entered politics through local body affairs, serving as a member then chairman of the Tiki Highway Board. From 1877 to 1886 he was the first chairman of the Coromandel County Council. In 1881 he was elected to Parliament to represent Coromandel, retaining the seat in the 1884 and 1887 elections. He won the enlarged seat of Thames in 1890. Cadman married Fannie Bell at Whangarei on 15 April 1886; they were to have a daughter and two sons before Fannie's death in 1892.
Cadman was initially identified as a supporter of Sir George Grey. Unlike Grey, who was embittered at being omitted from the cabinet, he supported the second Stout–Vogel ministry from 1884 until its defeat in October 1887. He was a member of the caucus that elected John Ballance as leader of the opposition in July 1889, and from then on was firmly identified with the Liberal cause.
In his first years in Parliament Cadman seems to have made no great impression. He was a 'quiet, pleasant mannered man, who only spoke when he had something to say.' What he did say was well and sometimes forcefully expressed. His principal contribution to parliamentary proceedings was to ask questions on local or mining issues, particularly on the long-lasting campaign that Richard Seddon ran to abolish the duty on gold. Nevertheless, Cadman represented important elements in the Liberal alliance. His business interests and local body activities had enabled him to develop a network of contacts among the numerous and often isolated townships and rural districts of his electorates. He had, therefore, much in common with the country Liberals' emphasis on building roads and bridges and facilitating closer land settlement.
But goldminers and timber workers were the dominant groups in the Coromandel, Thames and Ōhinemuri electorates, and Cadman's horizons were therefore a little wider than those of the typical country member. Like Seddon, he seems to have had some – rather paternalistic – sympathy for labour reform. In 1886 he supported the movement for an eight-hour working day, although he believed it would be better established by custom than by law. He also initially supported the extension of the franchise to women, but later cooled towards the idea because of the uncertain political consequences; he did, however, vote in favour of it.
One issue about which Cadman had decided opinions was the question of Māori lands, which was clearly bound up with his commitment to closer land settlement. Following the election of the Liberal government in 1890, Premier John Ballance took the native affairs portfolio and set up the Native Land Laws Commission headed by W. L. Rees. The commission produced a scathing indictment of the Native Land Court for not recognising the tribal principle in Māori land tenure. It also proposed involving Māori owners in the management of their lands, recommended a native land titles court to validate disputed titles, and, with James Carroll dissenting, favoured resuming Crown pre-emption, a measure which Cadman personally supported.
On 4 February 1891 Cadman was appointed native minister. He made various economies in departmental expenditure, including ending a commission which had been set up to investigate and validate Māori land titles, and dismissing several Native Land Court judges. Early in 1891 he decided against the recommendation of the Rees commission that Māori should be involved in the administration of their lands. Cadman's solution was to codify Māori land law, vastly extend the powers of the Native Land Court and abolish the Native Department.
He started on the process of abolishing the Native Department by repealing the Native Districts Regulation Act 1858 and the Native Circuit Courts Act 1858, which had provided much of the legal basis for the department's independent jurisdiction over Māori communities. In August 1891 he introduced an omnibus bill that attempted to codify Māori land law. He had a bitter tussle with Rees and, more quietly, James Carroll, during the select committee hearings. Cadman refused to make any compromises and the committee eventually recommended that the bill be postponed until next session. Both it and the Native Land Court Bill were defeated. Ballance, disconcerted with these defeats, in early 1892 considered replacing Cadman with Carroll.
Cadman, however, had his supporters. Seddon went out of his way to praise his administrative ability, and the Auckland Liberals, including his old mentor Sir George Grey, raised an uproar about the proposed reshuffle. They held Carroll to be unsuitable because he favoured leasing rather than selling Māori land. Ballance appointed Carroll to cabinet in March 1892, but only as member of the Executive Council representing the native race, a position that held no ministerial responsibilities.
In 1892 Cadman was able to pass the Native Land (Validation of Titles) Act and to begin dismantling the Native Department. The Native Land Purchase Office was transferred to the Department of Lands and Survey in June. The Native Land Court and a handful of clerks and interpreters that represented the rump of the old head office were transferred to Cadman's other portfolio, justice, in December.
In 1893 Rees charged Cadman with speculating in Māori lands in Hawke's Bay. Cadman strenuously denied this: he sued for libel and was awarded nominal damages. In a quixotic gesture he challenged Rees to join him in resigning his seat and putting the issues to the people in one of the electorates. Rees accepted and nominated his own constituency. They duly resigned and Cadman beat Rees by a majority of 751, one of the largest majorities ever gained before the extension of the franchise to women.
When Cadman returned to Parliament in 1893, he declined the offer of his old portfolio of native affairs. He retained justice and became minister of mines. As minister of justice he completed the dismantling of the Native Department system by repealing the Resident Magistrates Act 1867 that had allowed Māori assessors an advisory role in judicial proceedings. In its place, the Magistrates Court Act 1893 created stipendiary magistrates with strictly judicial functions. The passing of this act brought Māori communities completely under the judicial and police systems. As minister of mines Cadman introduced little that was new. He consolidated the Mining Act in 1898 and was responsible for buying and making available a patented gold extraction process that it was hoped would boost the industry by making smaller claims more profitable.
Cadman was appointed minister for railways in 1895, an appointment which brought about a resumption of government management after a period of control by commissioners. The Liberal cabinet could now better co-ordinate its policies of land settlement, public works and employment. The railways were seen as agents of settlement because of their ability to transport farm and other goods conveniently and cheaply, and to supply new settlers on small-holdings. Cadman's task was to develop these policies as economically as possible. He had also to introduce a replacement policy for locomotives and to arrange for the carrying out of neglected maintenance work.
By 1899 he was able to point to major achievements. He had raised the return on investment, increased the number of miles of railway in operation, and overseen a rise in revenue. Tonnage had increased substantially and various tariff concessions had been made, the most important being the free cartage of lime for farmers. Employees were better treated: the wages of the lowest paid had increased, the new classification system provided extra remuneration for various categories of employees, and there was now a system of insuring casual labourers against accidents. Cadman had also decided not to increase the permanent staff but to share out the work as far as possible among the unemployed. Finally, rail travel had been made affordable by the provision of excursion fares.
In 1899 Cadman's health, never robust, deteriorated, and he was absent from Parliament for long periods. He resigned his seat in November, but Seddon appointed him to the Legislative Council in December and left him on the Executive Council as minister without portfolio. He resigned in April 1901, and was appointed a CMG that year and KCMG in 1903. In July 1904 he was elected Speaker of the Legislative Council. He died at Auckland on 23 March 1905.