GroenLinks-PvdA senator Mei Li Vos is the new chairwoman of the upper house after seeing off rivals from both coalition parties.

Vos, 55, was a surprise choice after the front-runner, Ilona Lagas of the farmers’ party BBB, withdrew following a disastrous first round in which she won just 14 votes from the 75 senators.

Vos then beat VVD contender Tanja Klip-Martin by 39 votes to 33 in a second ballot, with three senators abstaining. She said she was “pleasantly surprised” by the outcome.

Vos has been temporary chair since her predecessor, Jan Anthonie Bruijn, was appointed health minister by the VVD in a reshuffle of the caretaker cabinet, after centre-right party NSC pulled out of the coalition in August.

Lagas had been seen as the likeliest successor, but the BBB has been weakened by internal strife and defections which has seen it overtaken as the largest group by GL-PvdA.

Three of the 16 BBB senators elected in 2023 – the upper house is indirectly chosen by the provincial governments – have switched camps, with one moving to D66, another joining the far-right Forum voor Democratie and a third sitting as an independent.

Lagas also had to fend off competition from two other BBB candidates for the job before the election.

Right-wing parties were reluctant to back her, but the 10 senators for PVV, FVD and JA21 were also reluctant to back Klip because the VVD was instrumental in steering through the so-called “spreading law”, which enables the minister for asylum to force local councils to accommodate refugees.