|Full name||Seamus Anthony Brennan|
|Date of birth||6 May 1937|
|Place of birth||Manchester, England|
|Date of death||9 June 2000(aged 63)|
|Height||5 ft 10 in (1.78 m)|
|Playing position||Full back|
|1965–1970||Republic of Ireland||19||(0)|
|1970||League of Ireland XI||1||(0)|
|* Senior club appearances and goals counted for the domestic league only|
His first game for the club came in an FA Cup match against Sheffield Wednesday on 19 February 1958; this was United's first game after the Munich air disaster and Brennan scored twice on an emotionally charged night. He was playing as an outside-left in this game, the position left vacant following the death of David Pegg and the injuries to Albert Scanlon in the crash.
He helped United to the 1965 and 1967 Division One championships, as well as the European Cup. Born in Manchester, England, he played internationally for the Republic of Ireland, qualifying through his parentage—the first Irish international to qualify in this way. He retired from Manchester United in 1970 after playing 359 games and scoring six goals.
Brennan moved to Ireland where he became player-manager with Waterford United, winning two titles and three further international caps. He left at the end of the 1973–74 season.
He died, aged 63, after suffering a heart attack while playing golf near Waterford, on 9 June 2000 and was buried at his adopted town of Tramore. He was the first member of the 1968 European Cup winning side to die, the second being George Best in November 2005.
- Manchester United
- Football League First Division (2): 1964–65, 1966–67
- European Cup (1): 1967–68
- FA Charity Shield (2): 1965, 1967
- Waterford United
- League of Ireland (2): 1971–72, 1972–73
- League of Ireland Cup (1): 1973–74
- Top Four Cup (2): 1970–71,1972–73
- Texaco Cup (1): 1974–75