Some 2,000 security forces including riot police were deployed as marchers gathered from midday in warm early summer sunshine in the central Opera square for a protest dubbed a "Party for Macron", a tongue-in-cheek "celebration" of the 40-year-old centrist's first anniversary in power.
Smaller rallies took place in the southern cities of Toulouse and Bordeaux while the Paris variant kicked off with a mass picnic which drew numerous families.
Organisers had urged participants to attend in a party mood — but the high security owed much to hundreds of black-clad youths having torched cars and a McDonald's restaurant during traditional May 1st demonstrations in the capital, prompting fears that more "black bloc" protesters could hijack Saturday's
One protester held aloft a placard with the words "Mac-ron is disgusting," a play on words to show his feelings about the president and the fast food chain.
Organisers insisted the march from Opera to the Bastille area, east of the city centre, would be "joyful and festive."
'Worried about violence'
But government spokesman Benjamin Griveaux had expressed fears on Friday that the demonstration could turn violent.
He noted that the protest's name, the "Fete a Macron", can have a double meaning in French — either celebrating someone, or trying to do them harm.
"We are worried that there could be violence, and so we're reinforcing security measures," Griveaux said, adding the police role was to ensure peaceful demonstrations could go ahead.
Some supporters of the left-wing populist La France Insoumise party (LFI) brandished anti-Macron banners with slogans including "down with the president of the rich," "no to a social coup d'etat" and "for a Sixth Republic."
The protest is the latest in a series of large street demonstrations against Macron, whose overhauls of everything from the education system to the state rail operator have been causing friction with various groups.
The demonstration was organised by firebrand LFI lawmaker Francois Ruffin and other ex-members of the Nuit Debout (Up All Night) leftist movement that staged nocturnal rallies across France in 2016. Ruffin told AFP this week that Macron may have won a democratic election last May but "democracy does not mean shutting up for five years".
"People have the right to challenge him," said Ruffin, a journalist whose documentary "Merci Patron", about a poor couple who take on France's richest man, captured an angry zeitgeist and filled cinemas in 2015.
Numerous university faculties meanwhile remain blocked by protests against Macron's plans to make university access more selective, causing major disruption to students starting their summer exams.
And Friday marked the latest in a series of rail strikes as train drivers and other staff object to Macron's overhaul of the SNCF, aimed at reducing its massive debts and making it more competitive.
Many French leftists have called for Macron's opponents, from students to striking rail workers, to join forces in a re-run of the massive May 1968 protest movement that shook France exactly half a century ago.