J
- J. Keirn Brennan (1873–1948), American songwriter
- James Alexander Brennan (1885–1956), American songwriter
- Jack Brennan, a military aide to President Richard M. Nixon
- Jack Brennan (1863–1914), American baseball player
- Jacob Brennan (born 1990), Australian rules footballer
- James F. Brennan
- James Herbert Brennan
- Jared Brennan
- Jim Brennan is a Football (soccer) player
- John G. Brennan
- John O. Brennan Former NCTC Director, CEO of TAC
- Joseph Brennan (basketball) (1900–1989), American basketball player
- Joseph Brennan (civil servant)
- Joseph Brennan (Irish politician)
- Joseph Brennan (politician)
- Joseph Charles Brennan
- Joseph Payne Brennan (1918–1990), American poet/author; WWII Veteran, ETO
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