Publicist Teal Cannady said in a statement that the two actors separated over the summer after 23 years together, The Associated Press reports. She did not elaborate, saying, "No further comments will be made."
Sarandon, 63, and Robbins, 51, met while shooting the 1988 film "Bull Durham." She played a minor-league baseball groupie, while Robbins played a young, flame-throwing pitcher. They have two sons together, Jack, 20, and Miles, 17.
For a show business couple, Sarandon and Robbins were particularly admired for the length of their relationship - even though they never wed.
In 2004, she told the Times of London, "He is a guy's guy, and he is also 12 years younger than me. I won't marry because I am too afraid of taking him for granted or him taking me for granted - maybe it will be a good excuse for a party when I am 80. Our children and property bind us, but so does the battle. We fight strongly but fairly. I can't say that it is always comfortable, but he is my really good friend."
Both actors are well known for being liberal activists. The family attended President Barack Obama's inauguration in January, although Sarandon insisted in a recent interview with Psychologies magazine that "our dinner table conversations are rarely political."
The two have collaborated on several projects, including Sarandon's Oscar-winning 1995 portrayal of Sister Helen Prejean in "Dead Man Walking," which Robbins adapted for the screen and directed.
Sarandon was previously married to Chris Sarandon, whom she met in college. The actress also dated director Franco Amurri in the mid '80s. The two had a daughter, actress Eva Amurri, in 1985.
Sarandon currently stars in "The Lovely Bones," while Robbins last appeared in 2008's "City of Ember."
The split was first reported by People magazine.