Swinney joined the SNP at the age of 15, citing his anger at the way in which Scotland was being portrayed by television commentators at the Commonwealth Games. He involved himself in the SNP Youth Wing and gradually as time went by became more and more active in the party, becoming firstly the SNP Assistant National Secretary and then the National Secretary.
At the time of the 1990 leadership contest he supported Margaret Ewing in her bid to become SNP leader, but this did not stop him becoming politically close to the man who would win that contest, Alex Salmond.
In 1997 he was elected an MP for the North Tayside constituency, and in 1999 he was elected to represent the same area to the Scottish Parliament. He stood down as a Westminster MP at the 2001 election in order to avoid splitting his time.
The leadership contest the following year was marked by serious argument between the SNP Gradualist wing of the party, who in the main supported Swinney and SNP Fundamentalist wing, who in the main supported Neil. Swinney won the contest but the media raised some doubt about his ability to lead following poor SNP performances in the 2001 UK General Election and the 2003 Scottish Parliamentary Election.