Former French education minister Benoit Hamon
Hamon comfortably beat Valls in the run-off vote to clinch the party's nomination. Valls conceded defeat before the final tally was announced when after 60 percent of the votes counted showed Hamon had just over 58 percent to Valls' 41 percent.
However, Hamon, 49, is not expected to perform quite as well in the presidential poll as the outgoing Socialist president Francois Hollande's approval ratings continue to dip.
The election favorite, right-wing candidate Marine Le Pen, Francois Fillion of the Conservative party and centrist Emmanuel Macron all lead the polls over Hamon.
Hamon's proposal for a universal monthly income for all citizens and calls to legalize cannabis made him by far the most left-leaning candidate out of the initial seven Socialist campaigners, and resulted in his subsequent popularity spike.
Hamon's other proposals include a 32-hour working week, abolishing the labour law passed last year that made it easier to hire and fire employees, a tax on artificial intelligence and robots, increased public spending and a widening of the deficit to invest in renewable energies.
Even those who were not members of the Socialist Party were allowed to vote in the primary, resulting in a turnout higher than the previous week when 1.6 million people cast their vote, organizers said. However, the accuracy of number has been called into question after journalists at Le Monde and Buzzfeed reported that they were allowed to vote multiple times.
Hamon unceremoniously interrupted Valls just minutes into his concession speech to accept his victory, forcing television stations to interrupt their live feed of Valls to cut to the winner.
Some unimpressed voters took to social media to lambaste Hamon as rude, vengeful and "shameful" for the unfriendly move.
Others labeled it a "cordial misunderstanding" and lack of communication between party coordinators.
Why is it somehow 'left wing' to want to be part of The EU?
I was watching a speech by Marine Le Pen a while ago, and I couldn't help thinking that this left wing/right wing thing is pretty much a make-it-up-as-you-go-along affair.
All the things Le Pen was talking about were like echoes of the British Left from the time of my youth. The post-war, trade union dominated Labour movement in Britain was pro-jobs for British workers, anti-mass immigration, anti-European single market. It was the 'right wing' Conservative Party who brought about heavy immigration and pushed Britain into, first, The Common Market, and then The EU.