Germany's Social Democrats (SPD) - junior coalition partner to Chancellor Angela Merkel's Christian Democrats (CDU) - agreed Monday to back the EU-Canada trade deal CETA after some convincing from their party leader.
The majority of around 250 SPD delegates at a party conference in Wolfsburg voted to support the controversial deal, dpa has learned.
Critics say the deal to eliminate 98 per cent of tariffs, allowing the free flow of goods and services between Canada and EU member states, would give multinational corporations undue power in European markets.
SPD leader and Vice Chancellor Sigmar Gabriel brought sceptics from his own ranks on board by promising greater inclusion for national parliaments and other interest groups in the negotiating process.
The party did not give an exact breakdown of the result. Gabriel said two-thirds of the delegates came out in favour of CETA.
Gabriel has been a vocal proponent of the deal and Monday's vote was interpreted as a referendum on his hopes of challenging Merkel in next year's general election.
Merkel's governing coalition requires the support of the left-leaning SPD in order to support CETA. The party's vote to back the move keeps EU officials' push for its temporary implementation in late October on track.
The vote comes as public support for CETA and the much larger Transatlantic Trade and Investment Partnership (TTIP) between the EU and the US is flagging on both sides of the Atlantic.
Some 320,000 people rallied against the trade deals in Berlin, Frankfurt, Cologne, Stuttgart, Hamburg, Leipzig and Munich on Saturday.