Brosnahan, Seán (1911–87), teacher and trade unionist, was born 26 August 1911 in Killaloe, Co. Clare, one of nine children of John Brosnahan, RIC sergeant, and Norah Brosnahan (née Ryan) (d. 1946). One of his brothers was Thomas J. Brosnahan (d. 1996), catholic archbishop of Freetown, Sierra Leone. Between 1911 and 1920 the family lived in Corofin, Co. Clare, and Tralee, Co. Kerry. Educated at the CBS Tralee and St Brendan's College, Killarney, Seán trained as a teacher at the De La Salle teacher training college, Waterford (1931–3), and then moved to Dublin, where he worked in various CBS schools until 1961. After enrolling as a night student at UCD, he graduated BA and subsequently received an H.Dip.Ed. (1940); he later graduated MA in educational science (1941). In 1953 he obtained a diploma in public administration.
In 1945 he was elected chairman of the Dublin city branch of the Irish National Teachers’ Organisation (INTO), which represented primary school teachers, and was to the fore in the teachers’ strike administrative committee during the bitter seven-month dispute of 1946. Incensed by the union's decision to call off the strike without securing a rise in salaries, Brosnahan, Matt Griffin, and their supporters successfully challenged the union's hierarchy for the elective posts. Brosnahan served as president in 1947–8 and dominated the INTO for the next thirty years, joining the INTO staff as treasurer (1961–7) and general secretary (1967–78).
In 1952 vocational teachers, represented by the Vocational Teachers’ Association (VTA), were awarded parity in pay with secondary school teachers. The INTO was incensed and Brosnahan spent much of the next two decades leading the crusade for parity of pay among teachers. Remembered as the ‘INTO's most notorious firebrand’, he was instrumental in establishing the union as one of the most effective lobby groups in the state. He was a formidable advocate, and worked for the abolition of the rating system by which teachers were assessed as well as securing degree status for the three-year teacher training course. He also pioneered closer links with other teaching unions, at home and abroad, and was a member of the ICTU executive for thirteen years.
Under Brosnahan's leadership the membership of the INTO doubled to over 20,000, making it the largest of the three teaching unions, and in 1969 he was made an honorary fellow of the Educational Institute of Scotland. In the area of special education he was instrumental in establishing the diploma in special education at St Patrick's College, Drumcondra, Dublin. At UCD he secured INTO funding to establish in 1958 the first full-time course in psychology. Using his political influence he saw the establishment of a government commission of inquiry on learning disabilities (1961–5) and within the Department of Education the establishment of a section devoted to special education.
Brosnahan sat as an independent in the seanad for the labour panel (1961–77) and in 1973 became the only independent member of the oireachtas to be appointed as a substitute representative of Ireland to the consultative assembly of the Council of Europe. He was a founding member, first treasurer (1961), and president (1978–9) of the National Association for the Mentally Handicapped of Ireland and was also a director of the National Rehabilitation Board and a member (1977–87) of the board of the Educational Building Society. A keen GAA footballer in his youth, he won two Dublin county championship medals with Clann na Gael. On 14 September 1950 he married Shiela Margaret Quinn, a national teacher, of Park street, Monaghan. They had three sons and one daughter and the family lived at Santanno, 13 Danielli Drive, Artane, Dublin. Brosnahan died 9 December 1987 at St Joseph's Hospital, Raheny, Dublin. The Sean Brosnahan Memorial Fund for Research into Learning Disabilities was established in his honour and as recognition of his work in this area.