Jam-maker and devout PM layman, he used his considerable wealth and influence to promote the advancement of the PM Connexion. Born in Colne, Lancs, on 23 February 1846, he worked for a short while in the little family shop, before commencing business on his own in 1862. His home-made jams were so successful as to encourage him to open a small factory in Bootle (1874) before transferring to extensive premises at Aintree (1886), with an additional factory in Southwark, London from 1901. A conscientious and paternalist employer, he built a model village for his employees at Aintree and in 1889 introduced a profit-sharing scheme.
A private vow on New Year's Day 1877 to devote a tenth of his gross annual income to religious and charitable purposes proved a landmark in his career and in his later years he was giving away up to a third of his entire income, while also encouraging the recipients of his generosity (especially the PM Church) to give more willingly themselves. The major beneficiary was the Theological Institute in Manchester, known from 1906 as Hartley College and he was largely responsible for the recruitment of A.S. Peake to its staff in 1892. He also financed the purchase and adaptation of Holborn Hall as the connexional PM headquarters and gave generous support to the work of Thomas Jackson in Whitechapel, London.
His influence on PM was evidenced in many other ways, including the establishment in 1890 of the Chapel Aid Association, of which he served as Chairman and Treasurer until his death. He was the only layman to be elected as President of the PM Conference (in 1909). He was also a generous benefactor to Colne, providing almshouses (1911) and a hospital, opened by his daughter in 1924. He was knighted in 1908 for his commercial and philanthropic work and was Vice-President of the 1892 Conference and President in 1909. He was the nephew of Robert Hartley (1817-1892; e.m. 1835) and among his sons-in-law were the PM minister Joseph T. Barkby and J.S. Higham MP. He died at Birkdale, Southport on 25 October 1922. A Hartley Memorial Fund was launched to support the training of medical missionaries and needy stundents and a bust of Sir William was placed in Hartley College.
His only unmarried daughter, Christiana Hartley CBE (1872-1948), was active in the public life of Southport, as a member of the town council and its first female mayor in 1921. She built and equipped a maternity hospital in Southport, opened in 1932. She also served on the Ormskirk Board of Guardians and in 1927 was given the freedom of her native town of Colne.
The family firm survived two world wars, but in 1959 became part of the international food and drink empire Schweppes.
Peake dedicated his book Christianity its Nature and its Truth to him as 'large-hearted in Philanthropy, fertile and sagacious in counsel, faithful in the stewardship of wealth'.