William Reeves was born in Clapham, Surrey, England, probably on 10 February 1825, the son of Jane Elizabeth Lamb and her husband, William Reeves, a civil servant. He was educated privately, worked as a bank clerk and became a member of the London Stock Exchange. On 21 April 1853, at Clapham, he married Ellen Pember, daughter of J. E. R. Pember, a rich and influential Stock Exchange member. There were to be 11 children of the marriage, eight of whom survived infancy.
About 1854 Reeves suffered a financial setback; he defaulted from the exchange and although readmitted, decided to emigrate. He arrived with his wife and a young daughter in Wellington, New Zealand, on the Rose of Sharon on 19 January 1857. The family settled in Canterbury, where they quickly became part of the influential circle that included Crosbie Ward, Charles Torlesse and W. J. W. Hamilton. Reeves was successively a customs clerk, a farmer at Rangiora, the manager for Torlesse's Fernside run and a carrier between Heathcote and Lyttelton. In 1860 he bought C. C. Bowen's share of the Lyttelton Times and became the newspaper's manager. After Crosbie Ward's death in 1867 he became editor.
Between 1867 and 1875 Reeves was involved in politics, failing conspicuously in his term as resident minister for the Middle Island (South Island) in William Fox's ministry of 1869–72. In 1874 he split with Julius Vogel over the abolition of the provinces and became an ardent champion of Sir George Grey. He lost his seat at the 1875 election but in 1884 was called to the Legislative Council.
Reeves's principal work was the ownership of the Lyttelton Times. During the 1870s it remained the most fiercely provincialist of newspapers, but by the late 1880s had matured into the country's leading advocate of liberal political ideas. He supported Donald McLean's paternalistic Maori policy of 'sugar and blankets'; took a 'sympathetic and humane' view of the needs and rights of workers; understood the need for protection of domestic industries in a young colony; supported Vogel's programmes of public works and immigration; and advocated closer land settlement. The paper also included contributions from William Gisborne, R. A. Loughnan (editor from 1875), and, after 1880, Reeves's son, William Pember Reeves. He also guided the Lyttelton Times Company newspapers during their prolonged battle with the Press Company during the 1870s and 1880s. Their financial problems were compounded by his own heavy mortgage commitments on his fine Opawa property, Risingholme; invariably hard-pressed, he was virtually bankrupt by 1891.
Reeves helped found the United Press Association and was its first chairman of directors, and was a director of both the Union Fire and Marine Insurance Company of New Zealand and the Mutual Life Association of Australasia. He was also a governor of Canterbury College, president of the Christchurch Musical Society, a Canterbury Jockey Club steward, a founder of the Canterbury Club and owned several successful racehorses.
William Reeves was a complex man. Inside his family and with employees he was affectionate and very much loved. He was well read and fond of music. His liberal views deeply influenced his son. As a leader writer, however, Reeves was aggressively partisan and venomously vindictive towards opponents. In public his reserve and sensitivity made him a poor speaker and an ineffectual debater, giving an impression of cold aloofness. He fastidiously disliked political life, adopted 'an austere official manner' and cultivated 'a gift of sharp speech'. William Rolleston described him as 'a very honestly intentioned man, but bitter.' He died at Christchurch on 4 April 1891, survived by his wife and eight children. Ellen Reeves died at Christchurch on 3 March 1919.