 On 12 January 2017, Mélenchon secured the 500 elected sponsors required to be validated by the Constitutional Council.After Benoît Hamon won the nomination for the Parti Socialiste on a left-wing platform, beating former Prime Minister, Manuel Valls, 58–41, Hamon announced on TF1 on 27 February that he and Melenchon had been in talks to form an alliance, but their stances on the European Union separated them, as Melenchon's platform was to renegotiate EU treaties or hold a referendum.France 24 reported following this that, "Adding their scores would place a candidate in first or second place"

Jean-Luc Mélenchon held at a consistent 12% for most of the campaign, until a late upwards surge which put him just behind third place Francois Fillon at 18%.