Ossinovksi stated that he made the decision once the March 3 general election were clear. SDE won 10 seats at the election, down from the 14 they had at in the closing months of the XIII Riigikogu (after Urve Palo left the party), polling a little over 55,000 votes, or just under ten percent of total.

The party made overtures to the election-winning Reform Party, which the latter took them up on later, but the 44 seats that the two parties together held was not enough to get a majority at the 101-seat Riigikogu, even as President Kersti Kaljulaid nominated Reform leader Kaja Kallas prime minister.

Ossinovski became SDE leader in May 2015, while he was education and research minister, later becoming Minister for Health and Labour, which he stood down from in May last year, handing over to Riina Sikkut.

"Over these past four years, I have given all I had to give in standing for our party and social democratic values [and] put all my knowledge and all my energy into it. I thank everyone who has provided advice and support to me during that time. There have been many of you, and your support has been invaluable," Ossinovski said on Monday, adding it was now time to hand over the baton.

"I am convinced that there will be no shortage of candidates at chair this time. This is very good,'' he continued.

''After the longest uninterrupted period of time in history that socialists have been in the government, it is of utmost importance to hold a debate on different visions for the future. I hope that this discussion will be profound and substantive, enabling the party to make the right choice on June 9. Let us have success with that!" he went on, noting the importance of focusing on strong results at the European elections in May. 

"Our number-one candidate, the unrivaled Marina Kaljurand, is the candidate most supported by the people. An opinion poll published today shows that we are catching up with the two leaders when it comes to support. Let us do this, so that open and passionate debate within the party will strengthen our European elections campaign," he went on.

He is set to remain leader until June 9, when the party board will convene, BNS reports.