Brosnan married Australian actress Cassandra Harris in 1980 and adopted her two children, Charlotte (born 27 November 1971) and Christopher (born October 6, 1972) after their father died in 1986. Brosnan and Harris had one son together, Sean (birth 13 September 1983). Harris died of ovarian cancer in 1991. In 2001, Brosnan married American journalist Keely Shaye Smith, and they have two sons together, Dylan Thomas Brosnan (birth 13 January 1997) and Paris Beckett Brosnan (birth 27 February 2001).

Brosnan supported John Kerry in the 2004 Presidential election and is a vocal supporter of gun control and same-sex marriage. An outspoken environmentalist, Brosnan was named 'Best-dressed Environmentalist' in 2004 by the Sustainable Style Foundation. Brosnan first became aware of nuclear disarmament at the age of nine when worldwide condemnation of the 1962 U.S. nuclear tests in Nevada headlined international news. During the 1990s, he participated in news conferences in Washington,