She was born in Croydon, the daughter of a soldier, and attended Selhurst Grammar School. She entered the civil service at age 17 in the Office of Population Censuses and Surveys, later marrying a Polish air ace, Stanisław Losinski in 1942, which informed her opposition to communism.
In 1975 she was elected President of the Civil and Public Services Association (CPSA) for the first time, beating her nearest rival by 10,000 votes, although she was deposed the following year. She re-took the position from 1979-82, the position going to Militant supporter Kevin Roddy in 1982, before Losinska was re-elected once more from 1983-86. Throughout much of this period she allied herself with Alistair Graham who became CPSA General Secretary from 1982-86.
Losinska's presidencies were surrounded by controversies. During the first year of her presidency she had taken the union's executive after they had censured her for her comments in an article in Readers Digest, where she had said the union was being infiltrated by Trotskyists and Marxists and wished to reply to her in the union's journal, Red Tape. As chair of the Solidarnosc Foundation she clashed with Arthur Scargill over his criticisms of Polish trade union Solidarnosc, and later appointed Knight Commander of the Order of Polonia Restituta. Her opposition to a merger with the Society of Civil and Public Servants in 1986 led to a split in the Moderate group into Losinska's National Moderate Group and the Democratic Moderate Group. She chaired the Trade Union Committee for European and Transatlantic Understanding, a body funded by NATO and the US Congress.
- Keleny, Anne "Kate Losinska: Activist who struggled for the future of trade unionism in Britain while fighting factions in her own union", The Independent, 25 December 2013; accessed 19 January 2014.
- Taaffe, P. The Rise of Militant Fortress Books: London pg.197
- "Kate Losinska obituary, The Telegraph, 16 January 2014
- Irish obituary notice for Kate Losinska; accessed 17 January 2014.