Chancellor Angela Merkel's Christian Democrats overwhelmingly approved a coalition deal with the Social Democrats at a special party congress on Monday.
Some 948 delegates of the Christian Democratic Union (CDU) voted in favor of forming a "grand coalition" government with the Social Democrats, versus only 27 delegates against.
The vote strengthened Merkel's position within the party, after senior party figures and the party's youth wing accused the deal of giving too many concessions to the Social Democrats.
Merkel responded to these criticisms by arguing that the CDU had to assume responsibility for Germany, and make compromises to open the way for a stable coalition government in the wake of last September's election.
"We had a hard struggle, we had to make compromises, but we also achieved many points," she stressed.
Merkel's conservative bloc CDU/CSU and the Social Democratic Party (SPD) reached an agreement earlier this month to form a coalition government, after a 136-day post-election stalemate.
The Social Democrats are currently holding a mini-referendum on the coalition agreement with the CDU and its sister party the CSU.
A postal ballot of the SPD's 460,000 members on the coalition deal began on Feb. 20 and will end on March 2.
The results will be announced on March 4, according to party officials.
