Luke Gardiner, 1st Viscount Mountjoy PC (Ire) (7 February 1745 – 5 June 1798) was an Irish landowner and politician.

He was the son of Charles Gardiner by his wife Florinda, daughter of Robert Norman.

On 3 July 1773 he married Elizabeth, daughter of William Montgomery, an MP for Ballynakill and later a Baronet.

Their children included a son, Charles John, and a daughter Margaret, who later became Countess of Donoughmore.

[5] Lord Mountjoy was killed in action at the age of 53, leading his regiment at the Battle of New Ross.