William Clegg played football for Sheffield Wednesday and England, as did his brother Charles who became president and chairman of the Football Association and was known as "The Napoleon of Football".
Clegg was the leader of the Liberal group on Sheffield City Council from 1895. In his early years, he campaigned for the municipalization of the tramways in the city, and then for the construction of council housing in the city. He was able to ensure that an estate was built at Wincobank, and a project to build 400 houses was begun in 1909. He also acted as the major financier of the local Liberal group.
Clegg was considered to be on the right of the Liberal Party and was associated with the Liberal League. He was opposed to socialism and was hostile to the Labour Party. From 1909, he began co-operating closely with the Conservative Party group on the council, and in 1920 the two parties formed the Citizens' Association, Clegg being its first leader.
He pursued low-tax policies at the expenses of cutting services and running up debts. He was an opponent of David Lloyd George's policies. The Association lost control of the council to Labour in 1926, who removed him from the aldermanic bench.
Their father, William Johnson Clegg, served as Mayor of Sheffield and was a solicitor who made his reputation helping the victims of the flood caused by the failure of the Dale Dyke Dam in 1864.