Niall O'Brien (2 August 1939 in Dublin, Ireland – 27 April 2004 in Pisa, Italy) was an Irish Columban missionary priest, notable for being falsely accused of and detained in the Philippines in the 1980s on charges of multiple murder.

As Negros was largely a feudal society, with power concentrated in the hands of a few landowners with the support of the military, this action led to him being branded a communist by the authorities.

He was defended together with the rest of the Negros Nine by attorneys Bobbit Sanchez and Senator Jose W. Diokno of the Free Legal Assistance Group (FLAG).

[citation needed] Rather than accept a pardon, which would imply guilt, the priests had the charges dropped against them in return for agreeing to leave the country.

O'Brien made a promise to himself and his God that, if he should return home safely, he would perform the ancient pilgrimage to Croagh Patrick, which he did at the end of July 1984.