When Kim Campbell succeeded Mulroney as Progressive Conservative leader and prime minister in June 1993, she kept Lewis in Cabinet as Solicitor General, and also named him Government House Leader. Both Lewis and the Campbell government were defeated in the 1993 general election. Following his political defeat, he returned to his law practice in Orillia, Ontario.
Lewis remained a supporter of the Progressive Conservatives through the 1990s. However, in 2000, he supported Tom Long's candidacy to lead the new Canadian Alliance, which was an attempt to merge the PC Party with the Reform Party of Canada. In July 2000, however, he insisted to reporters that he was a loyal supporter of Joe Clark's renewed leadership of the Progressive Conservative party.