Thomas McCarthy Fennell (22 December 1841 – 23 February 1914) was a Fenian political prisoner transported as a convict to colonial Western Australia.

Tried for treason in the Clare Assizes, on 15 July 1867 he was found guilty and sentenced to ten years' penal labour.

Fennell remained in the Western Australian penal system until March 1871, when he received a conditional pardon under a Royal Clemency announced by William Ewart Gladstone the previous December.

While there, he was approached by John Devoy about plans to rescue the military Fenians still in Western Australia's penal system.

Fennell actively contributed to fundraising efforts for various Irish causes, including the Kilrush monument dedicated to the Manchester Martyrs.