Sinclair, Elizabeth (Betty) (1910–81), trade unionist, was born 3 December 1910, into a protestant working class family in Hooker Street, Belfast. She was the third child of two sons and two daughters born to Joseph and Margaret Sinclair. Her father worked as a sawyer in Harland and Wolff shipyard, her mother as a reeler in Ewart's linen mills. She attended St Mary's Church of Ireland school, Crumlin Road, from the age of four until she was thirteen. She stayed for a time with her aunt in Leeds in 1923 where she finished her education and found a job in the printing trade. She moved back to Belfast in 1925 and worked briefly in boxmaking, after which her mother took her to Ewart's mill to teach her the trade. While working in the mills she became interested in trade unionism, and joined the revolutionary workers' groups on their foundation in 1930. When these amalgamated to form the Communist Party of Ireland (CPI) in June 1933, she became a member of its first central committee. At the age of 22 she was secretary of the outdoor relief workers' strike committee and gained a reputation for courage and determination during a strike.
She attended the republican congress in 1934, and the same year was a student at the Lenin international school in Moscow, acting as courier for the Comintern. Returning to Belfast in 1935, she was engaged in some of the most violent riots since the 1922 disturbances. During the Spanish civil war she helped organise ‘aid for Spain’. She continued to work in the mills from 1936 to 1940, representing the flax and other textile workers on the Belfast Trades Council. She was imprisoned in Armagh jail in 1940 for an article in Red Hand, the CPI's northern newspaper. After her release, she worked full-time as district organiser and party treasurer. She wrote a number of pamphlets on the position of women as they moved into the war industries, calling for equal pay, and for day and night nurseries. She was the first CPI member to attend the Irish Trade Union Congress as a delegate in July 1941 and was an unsuccessful communist candidate in 1945 for Cromac, south Belfast.
When a division developed in the CPI in 1946 she left Belfast to manage the Communist party bookshop in Bristol, returning in November 1947 as secretary to the Belfast and district trade union council, a position she held until her retirement in 1975. As well as co-ordinating trade union activity in the Belfast area, she conducted what was in effect a citizens' advice bureau in which her office was open equally to republicans from the Falls Road and unionists from Sandy Row. She was prominent in opposing the 1956 Stormont rent bill, and efforts to release republican internees imprisoned in connection with the IRA campaign of 1956–61. During the cold war she remained totally loyal to the USSR. She was the cause of a split in the Belfast labour movement during the 1955 May day demonstrations, when her presence on the official platform caused part of the demonstration to break away and hold a rival meeting.
She became involved with the Northern Ireland Civil Rights Association (NICRA) in the late 1960s, being elected onto the thirteen-person steering committee representing the Belfast trades council and chairman of the executive in 1968. She resigned on 7 March 1969, apparently in protest at NICRA's increasingly militant policies. True to her loyalty to the USSR, she refused to condemn the 1968 invasion of Czechoslovakia. On her 60th birthday in 1970 she received the medal commemorating the centenary of Lenin's birth.
Sinclair remained politically active during the final ten years of her life, but the style of her involvement changed as she retired from leadership positions. The short-lived Northern Ireland power-sharing executive appointed her to the supplementary benefits commission in 1974. She remained there until 1976, when she went to Prague as the Irish representative on the editorial board of the World Marxist Review. She came back to Belfast in 1977 but soon returned to Prague, remaining there until July 1979. She attended many international conferences and was one of a large delegation that attended the 25th congress of the Communist party of the USSR. There were events in her honour in Belfast, Dublin, Liverpool and London to celebrate her 70th birthday in 1980. She never married.
Sinclair died 25 December 1981, suffocating from smoke inhalation caused by a fire in her flat in east Belfast.