European Parliament President Martin Schulz has said he will not seek a third term and is returning to German national politics.
"I will not run as president of the European parliament for a third term next year, I will run for the German Bundestag as the head of the list of my party, the SPD, in North Rhine-Westphalia," Mr Schulz told reporters in Brussels, referring to the Social Democrats.
Some in Brussels have questioned whether Mr Schulz should go at a time of turbulence for the union since Britain's vote to leave in June.
It could leave all three main EU institutions led by the centre-right and see pressure on the position of European Council President Donald Tusk, who will chair negotiations on Brexit.
The former Polish prime minister's first 30-month term expires at the end of May.
Jean-Claude Juncker has a five-year term at the head of the executive European Commission, which runs until October 2019.
The centre-right and centre-left in the legislature formed an effective grand coalition after Mr Juncker defeated Mr Schulz in 2014 to be parliament's choice to run the executive commission.
Since then, Mr Juncker and Mr Schulz have formed a close partnership, notably in confronting a strengthening challenge from eurosceptics.
Mr Juncker has lobbied hard for Mr Schulz to stay as parliament president but the centre-right in the legislature, led by another German, Manfred Weber, insist their bloc, which is the biggest in the chamber, should now have the presidency.
Mr Schulz ran a bookshop in his native Aachen in western Germany before entering the European Parliament in 1994.
As speaker of the body since 2012, he used new powers granted by the 2009 Lisbon Treaty to increase the legislature's role in EU politics and has used the post to raise his profile at home.
Fine Gael MEP Mairead McGuinness has confirmed that she is putting her name forward to become the European People's Party's nominee to succeed Mr Schulz.
