Smith has long expressed concerns about the rifts in the party, and has this week moved to formally take on Corbyn.
But who is he?
Not such a new face
Smith joined parliament in 2010, inheriting the very safe Labour seat of Pontypridd from its long time incumbent Kim Howells. But that wasn't his first encounter with Westminster.
Between 2002 and 2005, he worked as a special adviser to Labour MP Paul Murphy, first while Murphy was secretary of state for Wales, and then when the MP moved to the Northern Ireland office.
Although Smith has referenced the fact he didn't vote for the Iraq war as a strength over fellow contender Angela Eagle, Murphy did support the controversial invasion while Smith was in his team.
The journalist who turned lobbyist
Before politics, Smith spent 10 years as a BBC journalist, working on Radio 4's Today programme, as well as the Welsh politics programme Dragon's Eye.
He also spent three years as UK head of policy for pharmaceuticals giant Pfizer.
The age of ambition
The Pontypridd MP has long been open about his ambition within the Labour party. Highly regarded on the backbenches, Smith told the New Statesman in 2015 that it would be “an incredible honour and privilege” to serve as leader.
A rapid ascent
In parliament he was rapidly appointed as Labour's shadow Welsh secretary by Ed Miliband following the resignation of Peter Hain, before he was promoted to the work and pensions brief by Jeremy Corbyn last year.
Smith has backed the renewal of Trident, and championed the cause of the Women Against State Pensions Inequality campaign, which demands protections form women affected by the increasing age at which they can take their state pension.
Burnham and Miliband
Described as a member of Labour's “soft left”, in the two previous party leadership elections, Smith backed Ed Miliband and Andy Burnham to win.