Vejjajiva, who faces the murder charge in connection with the 2010 political violence, was the only candidate in the election and received 98 per cent of the vote. Party adviser Banyat Banthatthan nominated his candidacy.
But party members remain divided over whether the democratic process should be respected, with the party taking part in the February 2 snap election, or if they should continue with street protesters, who are calling for political reforms to be implemented before another election can be held.
The protesters want Yingluck and her brother former premier Thaksin Shinawatra to be out of the politics of the country.
Democrat politicians resigned from parliament this month to join the street protests, which have been led by Suthep Thaugsuban, who was a deputy prime minister under Abhisit until 2011.
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The move prompted Yingluck to dissolve parliament and deepened a political crisis.
The Democrats must decide by December 27 if they want to register for the vote.
Protesters have demanding for Yingluck's resignation and handing over the government to an unelected 'People's Council'.
She also urged Thai people to go to polling booth on February 2.
Caretaker Interior Minister Charupong Ruangsuwan warned the government would not allow protesters to break the law by disrupting registration procedures for the general election.
Yingluck's brother Thaksin was overthrown in a coup in 2006 and is on a self-imposed exile in Dubai.