Slattery is of Irish descent and was raised Catholic. He attended high school at Saint Sebastian’s School in Needham, Massachusetts, and received a Bachelor of Fine Arts from The Catholic University of America in 1984.

Slattery is an avid athlete who both skis and surfs. He married actress Talia Balsam in 1998 (who also played his on-screen wife, Mona, in Mad Men); they have one son together, Harry Slattery. They live in SoHo, Manhattan.

Apart from his role on Mad Men, Slattery has had roles such as union organizer Al Kahn on Homefront; Senator Walter Mondale in the HBO miniseries From the Earth to the Moon; as political adviser Tommy Flannigan in the HBO series K Street; guest appearances as Will Truman’s brother Sam on Will & Grace; as Michael Cassidy, Amy’s estranged husband, on Judging Amy; politician Bill Kelley on Sex and the City; principal Dennis Martino on Ed; and college president Peter Benedict on Jack and Bobby. In March 2007, he began a series of appearances on Desperate Housewives portraying Victor Lang, Gabrielle Solis’s (Eva Longoria) second husband, until his character’s death in Season 4. In December 2009, Slattery appeared on The Colbert Report in a faux commercial advertising gold.

In 2015, Slattery portrayed journalist Ben Bradlee Jr. in the Academy Award-winning, Golden Globe-nominated drama film Spotlight, and also appeared in the Netflix comedy series Wet Hot American Summer: First Day of Camp, for which he earned a nomination for the Critics’ Choice Television Award for Best Guest Performer in a Comedy Series.