This year's march had as its official theme the fight against the far right.
But most of those taking part appeared to be celebrating the landmark law which will come into effect in October.
Some posters and placards denounced leaders regarded as homophobic, such as Russian President Vladimir Putin and US President Donald Trump.
Many marchers wore colourful costumes ranging from camp to comic to explicitly erotic. Some wore virtually nothing at all, despite the heavy showers that marked the start of the parade.
As the march passed Berlin's Brandenburg Gate, one young Hungarian named Marco, could scarcely contain his delight at the new law.
“In Germany everyone now has the right to marry, even gays and lesbians!” he said, elated.
“We are fighting for that in our country,” he said. “It is an inspiration for us in Hungary.”
But Matheus, a young German marching beside him, said: “With marriage for all, we have really moved forward, but there is still plenty of daily discrimination which is unacceptable.
“There still a lot to do, we have to stay visible, stay present and that is why we demonstrate, so there is even more equality.”
The main impetus to legalise same-sex marriage came not from Chancellor Angela Merkel but from her leftist rivals.
Merkel, although she personally opposed the move, gave her Christian Democrat deputies a free vote on the issue and the bill passed by 393 votes to 226 on June 30, sparking celebrations inside the Bundestag.
German President Frank-Walter Steinmeier signed the measure into law on Friday and it will come into force in October.
Merkel's political rivals, the Social Democrats on the left and the Liberals on the right, had made the issue a prerequisite for any alliance after the September 24 elections.
The reform also reflects German public opinion.
Polls show three-quarters supported granting full marriage rights to same-sex couples, who have since 2001 been allowed to live in so-called civil unions.