Paul was elected Liberal MP for Bodmin in 1974; in the October 1974 Election he increased the Liberal vote, but not sufficiently to withstand the swing. He subsequently worked for Shelter, managed a local newspaper group in the South West and, as a consultant, advised a variety of national environmental organisations.
Paul was elected MP for North Cornwall in April 1992 with a swing from the Conservatives of 6.5%.
He became Liberal Democrat Spokesman on Agriculture and Rural Affairs. At the 1997 General Election, Paul was returned with the largest Liberal Democrat vote and the largest Liberal Democrat majority. Promoted to Chief Whip and Shadow Leader of the House, he managed the 47-strong Liberal Democrat parliamentary team for the duration of that parliament.
After the 2001 General Election, Charles Kennedy reappointed Paul as Shadow Leader of the House to work with Robin Cook, pushing forward Liberal Democrat plans for the modernisation and reform of Parliament as well as overseeing the current business of the House of Commons. Paul served as a member of the Select Committee on Modernisation of the House of Commons from 1997 until 2005. With Ken Clark, Robin Cook, Tony Wright and Sir George Young, he prepared and introduced the second chamber of parliament bill.
Paul retired as an MP at the 2005 General Election and was subsequently made a life Peer. He is Liberal Democrat Lords Principal Spokesperson for Constitutional and Political Reform.