Friedrich Merz formally took over Monday as the leader of Germany's main opposition party, the center-right Christian Democratic Union of ex-Chancellor Angela Merkel, after his election was endorsed by a postal ballot.

The 66-year-old conservative, a one-time rival and longtime critic of Merkel, emerged victorious from a ballot of the party’s membership in December, beating two other contenders. He was endorsed by a party convention just over a week ago — a result that, for legal reasons, needed formal confirmation in a postal ballot. In that ballot, the party said Monday, Merz won 837 out of the 895 votes submitted.

Merz became party leader at his third attempt after predecessor Armin Laschet led the Union bloc, which the CDU dominates, to its worst-ever national election result in September. New Chancellor Olaf Scholz, whose center-left Social Democrats narrowly won, put together a three-party coalition that sent the conservative bloc into opposition.

Merz is already moving to consolidate his power. The head of the Union's parliamentary group, Ralph Brinkhaus, agreed last week to give up that post — the highest-profile job that the party has in opposition. Lawmakers are expected to elect Merz to that post as well on Feb. 15.

Merz said the new party leadership will "give all the support we can” to the party's contenders in four state elections this year. CDU governors in Saarland, Schleswig-Holstein and North Rhine-Westphalia — Germany's most populous state — are defending their jobs in votes between late March and mid-May. The party is the junior governing partner in Lower Saxony, which is due to vote in October.