John James Hayes (born 2 November 1973) is a retired Irish rugby union player who was the first man to make 100 appearances for his country.

In July 2011, Hayes was left out the 45-man Munster squad for the forthcoming season fuelling speculation that he may retire after the 2011 Rugby World Cup.

[3] Despite the speculation that Hayes would retire, he came off the bench for Munster in their opening Pro12 match against Newport Gwent Dragons in September 2011.

[9][10] Hayes won his first international cap against Scotland in 2000 and was Ireland's first-choice tighthead prop from then until the beginning of the 2010–11 season when he was replaced by Leinster's Mike Ross.

He was a member of the British & Irish Lions squad in their tour to New Zealand in 2005 and played in the warm-up test match vs Argentina.

He came on as a replacement against New Zealand Maori but was left out of the squad to play Australia, thereby losing his title of Ireland's most capped player to Brian O'Driscoll.

On 18 June 2009, Hayes was called up to the British & Irish Lions squad in South Africa as a replacement for the injured Euan Murray.