Lynn Walsh is a prominent figure of the Socialist Party of England and Wales, the English and Welsh section of the Committee for a Workers International, and editor of the Socialist Party's monthly magazine, Socialism Today.

Walsh joined the Revolutionary Socialist League (RSL) whilst a student at Sussex University when it established the Militant newspaper, in October 1964. Walsh soon became a contributor to the newspaper, his first article appearing in issue 9, published for September 1965. He became a significant figure in what became the Militant tendency, a Trotskyist entryist group within the Labour Party. Walsh was expelled from the Labour Party in 1983 together with Peter Taaffe, Ted Grant, Clare Doyle and Keith Dickinson, as one of the members of what was presented to the Labour Party as the 'editorial board' of Militant.

In the 1991 discussion on the "Open Turn", Walsh played a role in the joint preparation of the documents of the Majority faction, in which it was argued that the Labour Party had lost its working class base, with the result that Militant was isolated and without a basis of support against the pro-capitalist leadership. It was necessary, Walsh argued, at the 1991 Special Congress convened to discuss the issue, to take an "open turn", leave the Labour Party and start afresh "with an open banner". Of the original 'Militant editorial board', Peter Taaffe Clare Doyle and Keith Dickinson supported this 'Open turn' whilst its historical leader, Ted Grant, opposed it. After a Congress adopted the leadership's proposals by a majority of 93%, Militant Labour was created. This group later argued that the Labour Party had become so thoroughly a capitalist party that there was a need for the rehabilitation of the ideas of socialism, and changed its name to Socialist Party in 1997.