Armin Laschet, the chief of outgoing German Chancellor Angela Merkel's party, on Saturday took the rap for its worst ever poll result and said he would quit as the head of the country's most populous state.
The CDU's 16 years in power came to an end in the September ballot when it garnered only 24.1 percent of the vote.
"The responsibility for this result lies with me as leader and candidate for the chancellorship," Laschet told the CDU's Young Christian Democrats Congress in Munster.
The Social Democrats won the most votes and on Friday announced a preliminary deal to form a new coalition government with the Greens and the free-market liberal FDP.
If an agreement is reached, the Social Democrat Olaf Scholz should succeed Merkel as chancellor.
Laschet said the conservatives should now prepare to enter the opposition in the Bundestag, a position they have not had since 2005.
Laschet also said he would soon leave his position as president of the North Rhine-Westphalia region, the heartland of the CDU.
He called for a renewal of the party, through a generational change in leadership and greater involvement of women
Laschet also urged greater unity within the CDU, a call echoed by Health Minister Jens Spahn who spoke of a "a crisis of cohesion".
Spahn, 41, put himself forward as a candidate to "shape this new CDU", adding that it was for "the generation after Merkel to accept its responsibilities".
A day earlier, another potential candidate for the party, the ultraliberal Friedrich Merz, had warned that the CDU was "on the verge of collapse".