Thousands of people from across Poland brandished opposition Civic Platform placards and red-and-white Polish flags during the march through downtown Warsaw to the Royal Castle square on Saturday.
Donald Tusk, the leader of the Civic Platform, told the crowd at what organisers called the 'Blue March': "We are here to say loud what Poland feels ... We are here to say it is enough."
"We want early elections now," their banners read.
Opinion polls show more than 60 per cent of Poles believe that elections should be held and, according to most surveys, the Civic Platform would win them.
At a rival rally, 8,000 supporters of Jaroslaw Kaczynski, the current prime minister and leader of Law and Justice, and his twin brother Lech Kaczynski, the president, held banners reading "Solidarity in Poland".
Speaking to the crowd, Kaczynski argued that life is improving under his government, which took power a year ago.
He said: "In Poland, the situation is getting better, in all fields, from the economy to security.
"We want to protect this government, we want to protect a majority government because Poland very much needs such a government."
Three weeks ago, Kaczynski dumped the leader of the rural-based Self-Defense party from his cabinet, causing his government to lose majority support in parliament.
He immediately launched preliminary coalition talks with the opposition Polish Peasant's party.
But those collapsed two weeks ago after footage was broadcast showing a government aide offering an opposition politician a senior government post in exchange for joining Law and Justice.
The tape sparked fierce criticism of Kaczynski's party, plunging the government into crisis and increasing the prospect of early elections.
Opposition lawmakers accused Law and Justice of corruption and filed a motion for a vote to dissolve parliament, which would trigger snap elections if passed.
Senior lawmakers added the motion for the vote to the agenda of parliament's starting session on Tuesday. A vote could then be held on Friday.
If 307 of the lower chamber's 460 members support the motion to dissolve parliament, elections would have to be held within 45 days.
Law and Justice has enough votes to block the motion, but the prime minister has indicated that his party had not yet decided what it would do.