German President Joachim Gauck ratified the European Stability Mechanism (ESM) Thursday, removing the final obstacle to activate the eurozone permanent bailout fund.

Gauck's office said the president had signed a document "with which the treaty establishing the European Stability Mechanism will be ratified."

Gauck's ratification means legislation process of the ESM in Germany has been completed. The fund is now expected to come into force after a meeting by eurozone finance ministers set on Oct. 8.

Germany is the last country to ratify the 500-billion-euro (about 645 billion U.S. dollars) bailout fund. Though approved by German parliament June 29, the legislation of the ESM had been pending in Germany due to a court case challenging its constitutionality.

The Karlsruhe-based German Constitution Court rejected demand by plaintiffs to issue a temporary injunction to prevent Gauck from signing the treaties into law on Sept. 12, but set conditions protecting parliament's power.

As required, the parliament should "receive comprehensive information" over future decisions made by the ESM and Germany's financial burden in the fund should be limited to its share of the capital stock or 190 billion euros.

Increase of German liability in the ESM, if any, should not happen "without agreement of German representatives", and Germany must express that its interest should be respected in the ESM, reserve the right to opt out of mechanism.

Hours before Gauck ratified the ESM on Thursday, representatives from eurozone countries signed a joint declaration in Brussels to guarantee the ESM's compliance with German reservation.

"No provision of the Treaty may be interpreted as leading to payment obligations higher than the portion of the authorised capital stock corresponding to each ESM Member without prior agreement of each Member's representative and due regard to national procedures," said the declaration.

Eurozone countries also agreed that "providing comprehensive information to the national parliaments" should not be prevented.

The ESM was set to come into force in July 2012, but was suspended for months by complaints in Germany. The permanent bailout fund has a bailout capacity of 500 billion euros and is expected to work together with its predecessor, the European Financial Stability Facility, and the European Central Bank's open-end bond purchasing program to battle against the three-year-old crisis in Europe. (1 euro = 1.29 U.S. dollars)