Background
Born to a Church of Ireland family in the Ardoyne area of Belfast, Sinclair became a millworker alongside her mother after leaving school at the age of fifteen.
Born to a Church of Ireland family in the Ardoyne area of Belfast, Sinclair became a millworker alongside her mother after leaving school at the age of fifteen.
She then attended the International Lenin School in Moscow until 1935.
She joined the Revolutionary Workers" Group (RWG) in 1932. In 1933, she was involved in the Outdoor Relief Strike. The RWG established the Communist Party of Ireland (Consumer price index) in 1933, and Sinclair became a leading member.
The same year she became a full-time party worker in Belfast.
In the 1945 election for the Northern Ireland Parliament she stood as a Consumer price index candidate and received 4,000 votes. She stood for the group in Belfast Cromac at the Northern Ireland general election, 1945, taking almost one third of the votes.
In 1947, Sinclair was appointed full-time secretary of the Belfast and District Trades Union Council. Sinclair was the Trades Council"s representative at the talks which founded the Northern Ireland Civil Rights Association (NICRA) in 1967, and she served as NICRA chairperson until 1969, when she resigned, claiming it had become dominated by ultra leftists and was worsening sectarian divisions.
She stepped down from her trades council post in 1975, and moved to Prague to work for the World Marxist Review, before returning to Belfast.
She died in a fire in her flat in East Belfast in 1981.
When the all-Ireland Consumer price index dissolved in 1941, Sinclair remained an active member of the Communist Party of Northern Ireland (CPNI) and served as its Secretary from 1942-1945.