Undecided voter Amandine, 35, told RFI that she felt disillusioned with the French political system but was leaning towards Hamon because of his positive message, most famously a call for a universal basic income.
“Everybody is talking about terrorism; everybody is making us afraid of everything, and I think that’s not really the way … I think politicians should give us hope in the future and not make us afraid of everything," she said. "And I think Hamon is the only one right now who gives some hope – who is not so negative.”
Quentin, 28, wanted Hamon and hard-left candidate Jean-Luc Mélenchon to conclude a pact.
The two candidates “can’t win on their own”, he admitted but “they have the same ideas; the majority of their programmes are similar”, claiming that their views on the EU are not as divergent as many think.
While acknowledging that this is “the principal difference”, he claimed “they can find common ground” because “both of them want to renew the European management”.
Erstwhile Green party candidate Yannick Jadot, who has withdrawn in Hamon's favour, called for an "electoral insurrection".
"We can't be robbed of this election by means of renunciation and opinion polls," he told the crowd.
Polls currently put Hamon in fourth place behind the National Front's Marine Le Pen, centrist Emmanuel Macron and the mainstream right's François Fillon, although his vote combined with Mélenchon's could put him ahead of Fillon.
A pact between the two seemed unlikely this weekend, however, with Mélenchon holding a well-attended rally in Paris on Saturday and continuing to attack the record of the Socialist government.
Hamon, who is on the Socialist left and was a surprise winner of the party's primary, has failed to win the backing of some party leaders, including former prime minister Manuel Valls, who also stood in the primary.
Valls hit out at accusations of betrayal in an article in the Journal du Dimanche newspaper on Sunday, claiming that he had remained faithful to his principles in "rejecting the ambient cynicism where people promise everything and its opposite" and taking a swipe at Hamon's policies, such as the legalisation of cannabis and an increase in public spending.
"Some have left the ship as soon as the first wind blew," Hamon told the crowd on Sunday. "But I'm standing frim in the storm [...] These last few weeks have not shaken any of my conviction, they have confirmed them."
Paris mayor Anne Hidalgo appeared to be targeting Valls when she told the rally "One doesn't calculate, one doesn't hide behind some manoeuvre or other" and called on voters to cast their ballots for "our ideas, our values, our plans".
Education Minister Najat Vallaud-Belkacem was also among the party loyalists, telling the audience that Hamon was the candidate of "well-paid work, trained employees [...] the ecological transition, democratic renewal, a Europe that bases itself more on its citizens".
Macron in Germany
Macron, who is the current favourite to win the second round of the election, received an enthusiastic reception himself on Sunday ... in Germany.
Members of the Social-Democratic Party (SPD), formally linked to Hamon's party through the Socialist International, applauded their party's outgoing chair Sigmar Gabriel when he asked them to imagine Macron president of France and new SPD leader Martin Schultz chancellor of Germany after that country's parliamentary poll in September.
He was speaking at an extraordinary SPD congress in Berlin to elect Schultz as party leader and prepare for the election.
To read our coverage of France's 2017 presidential race click here