Billionaire financier George Soros has committed $1 million to the "Super PAC" group that is helping fund President Barack Obama's re-election bid, a person familiar with the pledge said on Thursday.

The move by Soros could trigger more big checks from liberal donors who have previously avoided giving to Super PACs due to their concern over the unlimited spending power of such groups.

Until this year, Soros held the record as the biggest contributor in an election cycle for his 2004 political giving. His record has been eclipsed by Las Vegas casino owner Sheldon Adelson, who has said he has given $70 million to help Republicans in the 2012 election. In the past Adelson has pledged to spend up to $100 million to defeat Obama and conventional democrats in upcoming elections.

Soros's $1 million pledge to Priorities USA Action was first reported by The New York Times as revealed at a big-donor meeting in New York on Thursday, held by the Democracy Alliance. The pledge was announced by Michael Vachon, a longtime Soros political adviser, according to the Times.

Soros also is set to donate $500,000 to two Super PACs backing Congressional Democrats, the newspaper reported.

With the donations, Soros now has given $4.3 million during this election cycle to PACs supporting Democrats, according to Politico -- the largest donor on the left, it said. Soros donated $24 million to outside groups ahead of the 2004 election, however.

In August, Priorities USA for the first time raised more than its Republican counterpart that backs Mitt Romney in his bid for the presidency. At the end of last month, Priorities USA had $4.8 million left in cash on hand, compared with the $6.3 million left in the coffers of the pro-Romney Restore Our Future.

Soros had remained largely on the sidelines of this year's Super PAC donations like many other Democratic donors who are uncomfortable with the notion of an unlimited-funding group that focuses predominantly on ads.

Super PACs can raise unlimited sums from corporations, unions and other groups, as well as individuals, and indirectly support a political candidate. They cannot by law coordinate with the candidate's official campaign.

Soros has estimated that in 2004 he spent $27.5 million, giving to outside groups in a failed effort to defeat Republican President George W. Bush.