Smith occasionally rebelled against his party in Parliament, on issues such as a third runway at Heathrow, the Government's renewal of Trident, and notably backed opposition Liberal Democrats motions on votes concerning the rights of Gurkhas to remain in Britain and the introduction of single transferable vote for elections.
In 2005 the Liberal Democrats came within 963 votes of winning the seat, with the drop in support for Labour widely attributed to the Iraq War, but in 2010 Smith secured a comfortable victory with a 4.1% swing to Labour, bucking the national trend. Similarly, in 2015, he was re-elected with 50% of the vote, an increase of 7.5% over 2010.
In the 2010 Labour leadership election, Smith supported Ed Balls. In the 2015 Labour leadership election, with minutes to spare before the deadline for nominees ended, he nominated Jeremy Corbyn despite not actually supporting Corbyn. Smith nominated Corbyn because he wanted a "broad debate" about the direction of the Labour Party. Smith was the 35th Labour MP to nominate Corbyn, which gave Corbyn the minimum number of votes he needed to appear on the ballot.