Eigenberg was born in Manhasset, New York, on Long Island, and grew up in Naperville, Illinois,[3] the only boy in a family of six children.

[5] After graduating from high school in 1982, Eigenberg enlisted in the United States Marine Corps Reserve, serving for three years (1982–1986), and was honorably discharged at the rank of Lance Corporal.

He appeared in the American TV show The King of Queens, in the episode entitled "Flash Photography", where he portrayed the groom of Carrie's annoying friend.

In 2002, Eigenberg starred as the short-lived character Officer Ross in the Season 3 episode of Third Watch, entitled "Superheroes: Part 1".

The on-and-off-again boyfriend and eventual husband to Miranda Hobbes (played by Cynthia Nixon), Eigenberg later reprised the role in both Sex and the City films in 2008 and 2010, and in the revival series And Just Like That... in 2022.