PARIS—Prime Minister Manuel Valls declared his candidacy for the French presidency, seeking to bolster the left’s electoral chances amid record-low approval ratings for the Socialist government he helped lead for the last 2½ years.
Surrounded by supporters on Monday, Mr. Valls cast himself as an experienced hand ready to stand against authoritarian and populist political forces that have risen around France.
“I want an independent France,” Mr. Valls said, “inflexible in its values faced with the China of Xi Jinping, the Russia of Vladimir Putin, the America of Donald Trump, the Turkey of Recep Erdogan. We need strong experience in this world.”
Mr. Valls is running as a centrist in the Socialist party amid a crowded field of candidates on the left. Yet his low approval ratings show his candidacy faces an uphill climb; opinion polls suggest he would lose easily in the first round of the general election to François Fillon, the top center-right candidate, and Marine Le Pen, leader of the far-right National Front.
Still, Mr. Valls is more popular than his boss, President François Hollande, whose decision last week not to stand for re-election cleared the way for Mr. Valls to run.
Mr. Valls said his candidacy would act as a bulwark against the possibility of Ms. Le Pen winning the presidency.
The extreme right “is today at the verge of power,” he said. “It would remove us from Europe, and from history.”
Mr. Valls also took aim at Mr. Fillon, whose sweeping program of economic liberalization helped push him to victory in last month’s center-right primary. Mr. Fillon has proposed to slash government spending, eliminate up to 500,000 civil-servant posts, raise the retirement age and cut taxes for the wealthy.
“I don’t want civil servants to work more to earn less,” Mr. Valls said, defending one of the Socialist party’s key constituencies. “I don’t want our children to have fewer teachers, that our cities and countryside have fewer police and gendarmes.”
Mr. Valls may have trouble emerging from the Socialists’ primary. He remains an unpopular figure within the left wing of the party, which he angered by championing a law to strip the citizenship of some French nationals who are convicted of terrorist crimes. Mr. Hollande backed away from that proposal amid stiff opposition from his own party and some on the right.
He also pushed a change to labor law that aimed to make it easier for French businesses to fire workers, further alienating party activists.
Among Mr. Valls’s main rivals for the Socialist nomination is the leftist Arnaud Montebourg, the former economy minister in Mr. Hollande’s government. If Mr. Valls wins the party primary, scheduled for the end of January, he would face another former minister, Emmanuel Macron , a pro-business economy minister who quit Mr. Hollande’s government in August after launching his own political movement.
Write to Matthew Dalton at Matthew.Dalton@wsj.com