Bruce was elected as the Vice-Chairman of the Scottish Liberal Party in 1975, in the same year he became a director with the Noroil Publishing House. He again stood for Parliament at the 1979 general election for the seat of West Aberdeenshire and was again defeated by the sitting Conservative and Unionist MP, this time Russell Fairgrieve by 2,766 votes. Bruce became the editor of the Aberdeen Petroleum Press in 1981 until his election as MP for Gordon in 1983.
Bruce stood for parliament for a third time at the newly created seat of Gordon, based largely on the former Aberdeenshire West. Fairgrieve retired, and at the 1983 general election he was very narrowly elected and became the Liberal MP for Gordon with a majority of just 850, and held the seat for thirty-two years. He was an outspoken opponent of coalition with the Labour Party.[6]
When he was elected to parliament, Bruce served on the Scottish Affairs Select committee, and in 1986 was given a job by David Steel as a Spokesman on Energy and Scotland. He also became Rector of the University of Dundee in 1986 for three years. After the 1987 general election, at which Bruce's majority had increased to 9,519, he was briefly a spokesman on Education, before speaking on Trade and Industry later in 1987. After the amalgamation of the Liberal Party and the Social Democratic Party and the formation of the Liberal Democrats he became the new party's Energy spokesman and at the same time became the Leader of the Scottish Liberal Democrats under the new leadership of Paddy Ashdown. In 1989 he was appointed as the Environment spokesman, before having the Scotland portfolio after 1990.
After the 1992 general election, at which he narrowly held Gordon by just 274 votes, he again became the Trade and Industry spokesman. By 1994 he had become the Treasury spokesman. Whilst a Treasury spokesman it was Bruce who developed the idea of a 'penny on income tax'. At the 1997 general election Bruce's majority had risen again to 6,997. The Liberal Democrats had 46 MPs, more than they have had since before the 1920s. Paddy Ashdown created a new Shadow Cabinet system and Bruce became the Liberal Democrat Shadow Chancellor of the Exchequer. When Ashdown stood down in 1999 he contested the leadership of the party but came in third place. In 1999, under the new leadership of Charles Kennedy, became the Chairman of the Liberal Democrats until 2001, and 2000 - 2015 was the president of the Scottish Liberal Democrats.
He married Veronica Jane Wilson in 1969 and they have a son and a daughter, before divorcing in 1992. Bruce married secondly, in 1998, Rosemary Vetterlein, a Lib Dem activist and prospective parliamentary candidate[11] who contested Beckenham unsuccessfully in 1997.
Lord and Lady Bruce have two daughters and a son together. Bruce takes a keen interest in deaf issues; one of his children is deaf.[12]