Liam Fox's first attempt to get elected as MP for a Scottish constituency was in 1987 when he contested Roxburgh and Berwickshire in the general election, but it ended in failure. He then to try and win constituency in England and was successfully elected as an MP for Woodspring in the 1992 general election.

A little over a year after his election in 1992, Fox was appointed Parliamentary Private Secretary to the Home Secretary, Michael Howard, in June 1993. These were then followed by appointments as Assistant Government Whip and Lord Commissioner of Her Majesty's Treasury following a government reshuffle in 1995. He was then Parliamentary Under-Secretary of State at the Foreign and Commonwealth Office from 1996 to 1997.

During his time in opposition, Fox was appointed Opposition Front Bench Spokesman on Constitutional Affairs In June 1997 and joined the Shadow Cabinet in 1998 as the principal spokesman for Constitutional Affairs. Between 1999 and 2003 he was the Shadow Secretary of State for Health.

Following the no confidence vote against the then Conservative leader Iain Duncan Smith in November 2003, Fox was appointed campaign manager for Michael Howard. When Howard then became party leader, Fox was made co-chairman of the party by Howard.

After the 2005 General Election he was promoted within the Shadow Cabinet to become Shadow Foreign Secretary.

In 2005, Fox announced he would join the contest to become the next leader of the Conservative party. In the initial ballot of Conservative MPs, on 18 October, he gained enough support (42 votes) to avoid coming last, and put himself through to the second ballot to be held two days later. He was eliminated with 51 votes in third place behind David Cameron (90 votes) and David Davis (57 votes).

On 7 December 2005 he was moved to Defence by new Leader of the Opposition David Cameron MP, before being appointed as Secretary of State for Defence in the Cabinet of David Cameron on 12 May 2010.

On 14 October, Fox's resignation as UK Defence Secretary was announced by the Ministry of Defence over his relationship with his friend Adam Werritty, who had described himself as an adviser to the minister without being on the government payroll or having security clearance.