Colonel Sir John McMahon, 1st Baronet (c. 1754 – 12 September 1817) was an Irish-born politician and Private Secretary to the Prince Regent 1811–1817.

By his second wife, Mary Stackpoole, his father has two other sons William and Thomas, who both achieved distinction.

He was succeeded in the baronetcy according to a special remainder by his brother General Sir Thomas McMahon, 2nd Baronet.

He undoubtedly used his position to benefit his family:[1] his half-brother William MacMahon obtained the coveted judicial office of Master of the Rolls in Ireland through John's influence, and he proved to be a popular and respected judge.

He had at least one sister Mrs O'Halloran, whose daughter married Richard Lalor Sheil, against her own family's wishes, and died young in childbirth.