The present school was formed in 1995 by the merger of Rydal School with the nearby Penrhos School for Girls, founded in 1880 by local Methodists. Both schools owed much to the initiative of the Rev. Frederick Payne. Penrhos was not a connexional school and its Methodist links were gradually eroded. Rydal Mount School for Boys was founded in 1885 by Thomas G. Osborn, formerly headmaster of Kingswood School. It became a connexional school in 1905, declined under his son George Osborn, but built up a strong academic and sporting reputation under his successor, Alfred J. Costain, headmaster from 1915 to 1946, who renamed it Rydal School. He is commemorated in the name of the Costain Building (1927). He was succeeded by Donald Hughes (1946-1968) and Peter Watkinson (1968-1991).
Famous old boys include the Tudor historian, Sir Geoffrey Elton and Wilfred Wooller, excused lessons to play Rugby for Wales and later captain of Glamorgan County Cricket Club, and the future Bishop J.W.E. Sommer of the German Methodist Church, who went there from Kingswood School in 1896 before going up to Cambridge. The school had strong links with the Bermondsey Settlement and the Old Rydalians support a boys' club in Liverpool. In 2003 there were around 600 pupils, including over 400 in the senior school.