Shirley Williams, one of the original “gang of four” Labour politicians who split to form the Social Democratic party, died peacefully in her sleep in the early hours of Monday morning, the Liberal Democrats have announced. Hailed by many as a trailblazer for a political career that spanned more than 50 years, she entered parliament as MP for the Hertfordshire town of Hitchin in 1964 and left it as Lady Williams of Crosby in 2016. Williams, who was 90, served in multiple prominent roles, including as education and science secretary under the Labour prime minister James Callaghan, and later became the first SDP member elected in a 1981 byelection in Crosby, Merseyside. She became president of the new party and supported its merger with the Liberals to form the Liberal Democrats, and was a stalwart who served as its leader in the House of Lords for three years from June 2001. As well as her career in Westminster, Williams spent time as a politics professor at Harvard University, as well as lecturing at Cambridge, Princeton, Berkeley and Chicago. She was married to the Harvard professor and historian Richard Neustadt, who died in 2003. Ed Davey, the Lib Dem leader, called the news of Williams’ death “heartbreaking for me and for our whole Liberal Democrat family”. He said: “Shirley has been an inspiration to millions, a Liberal lion and a true trailblazer. I feel privileged to have known her, listened to her and worked with her. Like so many others, I will miss her terribly. “Political life will be poorer without her intellect, her wisdom and her generosity. Shirley had a limitless empathy only too rare in politics today; she connected with people, cared about their lives and saw politics as a crucial tool to change lives for the better. “As a young Liberal, Shirley Williams had a profound impact on me, as she did on countless others across the political spectrum. Her vision and bravery, not least in founding the SDP, continues to inspire Liberal Democrats today. “Rest in peace, Shirley. My thoughts and prayers are with your family and your friends.” Layla Moran, the Lib Dem MP and former leadership candidate, said Williams was “an enormous personal inspiration” who showed her “kindness, humour and encouragement”, adding: “Mother of the SDP and the Liberal Democrat party, she was a trailblazing titan of politics. May she rest in peace.” Her colleague Alistair Carmichael described Williams as a “force of nature” who had a “razor-sharp political mind, personal warmth and enthusiasm that made her a natural campaigner”. Others from across the political spectrum also paid tribute to her, in a mark of how widely she was liked and respected. Boris Johnson said she would be “much missed”. The prime minister tweeted: “Sad to hear about Baroness Shirley Williams, a kind and thoughtful member of the once radical centre left. Even when we disagreed – as we often did – she had the gift of sounding so completely reasonable at all times. I spent many happy hours sparring with her on Question Time.” Keir Starmer also paid tribute. The Labour leader tweeted: “Very sad to hear of the death of Shirley Williams. She was widely respected across politics and was a tireless champion for the causes she believed in. She will be hugely missed.” Tony Blair said Williams was “one of the greatest social democrats of the last century, an immense figure of progressive politics through the decades, consistent in her commitment to equality, to social justice, to liberal social democratic values and to internationalism”. The former Labour prime minister added that even after Williams left Labour, many in the party still regarded her as a “source of inspiration and someone to look up to and admire”. The Conservative co-chair Amanda Milling said Williams’ political service was “remarkable” and served as “an inspiration for many young women looking to start a political career”, while the former Conservative chancellor Sajid Javid called her a “great parliamentarian that will be sorely missed”. The Commons Speaker, Sir Lindsay Hoyle, called Williams “one of a kind” who “loved elections … liking nothing better than engaging in debate with people and politicians”. Of the original gang of four, Williams is the second to have died, after the former Labour deputy leader Roy Jenkins died in 2003. Bill Rodgers and David Owen are still serving peers.