Guy Verhofstadt, leader of the ALDE group, announced that Barroso had succeeded in winning his group's support after making three statements which he described as "important".
The announcement came after Barroso was grilled by the Liberals in a behind-closed doors hearing in Parliament on Wednesday (9 September).
Verhofstadt said Barroso had promised to create a new commissioner portfolio for civil rights and fundamental freedoms, as requested by the Liberals. He also promised to put in place a single European supervision system for financial markets and launch a "big fight" for an own-resources increase in the next EU budget.
Barroso was told to repeat these three commitments in plenary before the full Parliament takes a vote on his candidacy, Verhofstadt said.
He also said he will ask a meeting of the Parliament's political group chiefs on Thursday (10 September) whether there is a need to hold a second vote on Barroso's candidacy after the Lisbon Treaty is ratified.
Under Lisbon, Barroso would need a majority of all 736 MEPs, while under the current Nice Treaty he would need the ballots of a majority of those present in plenary to be confirmed.
Greens 'don't understand' purpose of early vote
Meanwhile, the Green/EFA group, the only one which made its session with Barroso public, claimed there was no "rush" to vote on Barroso's re-appointment, and pleaded for a decision to be taken once the Lisbon Treaty is ratified.
During a hearing with the Portuguese, Green group co-chairman Daniel Cohn-Bendit said he had information that the Czech Constitutional court would decide rapidly on the treaty and overcome the last objections of a small number of senators who are close to Eurosceptic President Vaclav Klaus. In his view, the mandate of the present European Commission could be extended by three months, and the vote scheduled within this period, after the Lisbon Treaty is ratified.
Barroso responded that it would not be for the Constitutional Court but for Klaus to close the ratification process in the Czech Republic, and that his signature could not be taken for granted. He also objected to the Green group's tactics of campaigning under a 'Stop Barroso' ticket before discussing issues with the candidate.
"I don't want a Commission with a lame duck president," Barroso said. "If you are against me, vote against me."
Answering criticism that he had not done enough on climate change, Barroso said that the Commission's initial proposals were bolder than the final decision, which was taken after co-decision with the EU Council of Ministers and the Parliament.
"You're shooting at the Commission because it's easier. You're shooting at the wrong target," Barroso said.
