In Berlin, as in Munich, there was a sea of flags as people flocked to join the rallies despite the rain, carrying placards and banners representing dozens of anti-globalisation groups, NGOs, political parties and unions, AFP correspondents said.
"People are not letting their mood be ruined" by the weather, a spokeswoman for the organisers, Kathrin Ottovay, told AFP.
Roland Suess from anti-globalisation group Attac had earlier told AFP they expected 250,000 people to turn out in seven major German cities -- including some 70,000 in Berlin.
Some organisers put the national turnout as high as 320,000 while police put the figure at between 163,000 and 188,000.
Participants waved banners demanding "democracy instead of TTIP" and "share, don't divide."
The European Union and the United States began negotiating the Transatlantic Trade and Investment Partnership (TTIP) in 2013, aiming to create the world's biggest free trade market of 850 million consumers.
But the talks have become bogged down amid widespread in Europe that the deal would undercut the 28-nation bloc's standards in key areas such as health and welfare.
A new round of talks is due in October with US President Barack Obama hoping a deal can be concluded before he leaves office in January.
A smaller version of TTIP is also in the works with Canada, and that deal, called CETA, is due to be signed in October.
Exporters are in favour of the deal as it promises lower tariffs, less red tape and a wider base of consumers for their goods. But in Europe, consumers fear it would ride roughshod over the EU's labour market and environmental standards, and would bring about more outsourcing which would lead to job losses.
There are also concerns over plans for a special court to hear cases by companies against governments over breaches of regulatory issues, which opponents see as giving firms a veto over public policy.
"CETA and TTIP threaten environmental and consumer protection for millions of people in Europe and North America," said Jennifer Morgan, executive director Greenpeace International.
Not only the people, but European governments too are torn over the planned deals. The French government has put up strident opposition, with Prime Minister Manuel Valls demanding an end to the talks while the leader of Europe's biggest economy, German Chancellor Angela Merkel, voiced her backing for a deal.
In a recent interview, Merkel noted the high unemployment rate in several EU countries, and said: "we should do everything we can to create jobs -- the free trade agreements are part of that."
But even within her right-left "grand coalition", there is dissent. Vice-Chancellor and Economy Minister Sigmar Gabriel last month declared that talks on TTIP have "de facto failed". He had also insisted that "Europeans must not give in to (the Americans') demands".
EU Trade Commissioner Cecilia Malmstrom told Saturday's Bild daily she was aghast at the "misunderstandings, urban myths and outright lies in the debate" on the merits or otherwise of the treaty.
Suspicion is running high in Germany over the accords. "In Europe, they need to put people first ... that's why we must stop TTIP," said Berlin rally coordinator Axel Kaiser, representing a group of small- and medium-sized firms opposed to the deal.
A recent Ipsos survey found some 28 percent of respondents doubted if free trade could really bring benefits. More than half (52 percent) say it would lead to weaker standards and spawn increasingly inferior products.
Peter Gauweiler, who left the CDU and resigned as an MP in protest over Merkel's stance in the euro crisis, went as far as to call the proposed treaties "a danger for democracy".
Writing in the Sueddeutsche Zeitung, he denounced the proposed special court as a "form of secular sharia of capitalist managers".
But conservative daily Die Welt was more positive. "Before money can be distributed (to the population), it must first come in," wrote its columnist Daniel Eckert. "A further lowering of tariff barriers, the dismantling of bureaucracy and international standardisation are rather cost-effective methods to create greater wealth that future generations can benefit from," he argued.