Greens choose Peter
The Green party chose the 47-year-old Peter as a successor to Claudia Roth, with 564 of the 743 delegates at a party conference in Berlin voting in her favor.
Speaking before delegates, Peter promised to stengthen the party's profile and "win back lost trust."
"Self-assured, independent and without blinkers - that is where I would like to lead this party together with you," Peter said.
There was some opposition, with 11 percent voting against Peter's taking over from Roth, and 13 percent abstaining.
Earlier the Greens had said an emotional farewell to Roth as the party leader. She announced that she would not seek re-election to the co-leadership of the party after the Greens' poor showing in Germany's federal elections.
The joint leadership is a two-year mandate and always held by a man and a woman.
Pragmatist stays at top
The party's other co-leader, Cem Özdemir, was re-elected on Saturday. His challenger for the position, Thomas Austermann, had always been given little chance of winning by analysts. Özdemir - who comes from the party's "realo" or more pragmatic wing - secured the leadership role last year with a healthy 83.3 percent of the votes.
Özdemir won with 542 of the 759 votes cast.
On Wednesday, the Greens broke off coalition negotiations with Chancellor Angela Merkel's Christian Democrats (CDU) and their Bavarian sister party, the Christian Social Union (CSU).
The CDU and CSU won a resounding victory in the national elections, garnering 41.5 percent of the vote. The opposition Social Democrats rose from the 2008 elections, winning 25.7 percent.
The Greens, meanwhile, fell from the last federal election, dropping from 10.7 percent to 8.4. The loss placed them slightly behind the Left party, prompting a full-scale reshuffle of the leadership, with 22 politicians resigning.
A contentious tax proposal - a 49 percent levy on people earning at least 80,000 euros ($109,500) a year - was blamed for the loss of support. A further controversy, linking former party members to calls in the 1980s for some sexual acts between adults and children not to be treated as a criminal offense, also marred their image.
rc/mkg (dpa/AFP, Reuters)