She held several posts within the Glasgow Kelvin Labour Party from 1995—then the constituency of left-wing George Galloway. She was selected as a candidate (unsuccessful) for the 1999 European election. She was elected to the Commons at the 2001 general election for Glasgow Maryhill following the retirement of the sitting Labour MP, Maria Fyfe. She held the Maryhill seat with a majority of nearly 10,000. In the boundary changes which came into force for the 2005 election, Maryhill was abolished, and McKechin was elected for the newly drawn Glasgow North seat, but with a much reduced majority of 3,338 over the Scottish Liberal Democrats.
In Parliament she served briefly as the Parliamentary Private Secretary to Jacqui Smith in 2005 in her capacity as Minister of State at both the Department of Trade and Industry and at the Department for Education and Skills. She has also served on a number of select committees including; Scottish Affairs (2001–05) and International Development (since 2005). She replaced David Cairns as Parliamentary Under-Secretary of State at the Scotland Office on 16 September 2008.