The march held in the city's Victoria Square on Sunday was meant to demand a reversal of Britain’s ongoing plan to withdraw from the European Union.
The rally comes as the Conservative Party led by Prime Minister Theresa May is facing unprecedented internal divisions over the government Brexit strategy, Presstv Reported.
The protesters waved flags of EU and Britain while supporting calls for a second referendum on Brexit in which people could vote for their country to stay in the EU.
The Brits voted in favor of Brexit with a slight margin in an original referendum in June 2016.
The government and the opposition Labour Party have both rejected the possibility that there could be a second vote on the main issue of leaving the EU, as they insist that the results of the original referendum should be respected.
The Labour says a second vote would be possible but only on how Britain should leave the EU and whether a deal that could be signed between May’s government and Brussels would serve the interests of the Britons.
Tens of thousands were expected to attend the anti-Brexit rally in Birmingham just ahead of the opening of the Tory conference.
Protesters also staged a rally on the eve of the conference on Saturday to protest against Conservative Party’s continued commitment to austerity measures, which many believe has led to more poverty in Britain.
The Sunday demonstration is the latest to come from a series of rallies held against Brexit across the UK over the summer.
The protests will culminate in a massive march I n London in October. Britain will officially leave the EU in March.