Gallagher married Meg Mathews in Las Vegas, Nevada in June 1997. Mathews gave birth to a daughter, Anais, in 2000. Gallagher and Mathews divorced shortly afterwards, in January 2001, following Liam's own announcement of his separation from Patsy Kensit. He has since entered a long-term relationship with Scottish girlfriend, Sara MacDonald, who gave birth to Noel's second child, Donovan Rory MacDonald Gallagher in 2007. He is frequently a guest on The Russell Brand Show on BBC Radio 2.

Gallagher is an atheist., and has read "The God Delusion" by Richard Dawkins, saying, “Anything that disproves God, bring it on,”. He has also described himself as "a famous, wealthy, Irish, Catholic, working class, 'half an atheist and half a coward'". However, in 2005 Gallagher discussed his Catholic roots and how to pray with U2 singer Bono, saying of Bono "that he made tons of sense." Subsequent to his talk with Bono, Gallagher restated in a 2006 radio interview with Russell Brand that