Senior Liberal Democrat Baroness Shirley Williams is stepping down from the Lords in the new year after more than 50 years in parliament.
Lib Dem members including former leader Nick Clegg will gather for a reception tonight to celebrate her role in politics over the last six decades.
Lady Williams of Crosby, 85, first entered the Commons as Labour MP for Hitchin in 1964 and went on to hold several ministerial positions, including education secretary.
She was one of the “Gang of Four” MPs who broke away from Labour and founded the Social Democratic Party, and was its first president from 1982 until 1987 before taking a seat in the Lords in 1993.
She was Lib Dem leader in the Lords from 2001 to 2004.
At the reception marking her more than 50 years in Parliament, Mr Clegg and her fellow SDP founder Bill Rodgers will praise Lady Williams’s “outstanding contribution” to British politics.
Lord McNally, former leader of the Liberal Democrats in the Lords, said: “Throughout her life Shirley has made an outstanding contribution to the politics of this country.
“Her bravery, determination and commitment to her beliefs has benefited both parliamentary debate and public discourse for the last five decades.
“Shirley is a remarkable woman and it has been a huge privilege to work alongside her for all these years.”
A party spokesman said Lady Williams will be retiring in January and is expected to make a valedictory speech under new rules allowing peers to step down from the Lords, amid growing concern over the size of the House.