The pair split up in 1991 after seven years together. Downey Jr, 50 discussed about the meeting in New York during a radio interview, reported Us magazine.
While visiting the Big Apple, Downey Jr caught up with the Emmy winner, who was happy to meet up with her ex-boyfriend to talk.
The actor had earlier taken the responsibility for the break-up.
"I liked to drink, and I had a drug problem, and that didn't jibe with Sarah Jessica, because it is the furthest thing from what she is. She provided me a home and understanding. She tried to help me. She was so miffed when I didn't get my act together."
Downey Jr was able to get sober in the early 2000s after completing a stint in jail, and was married twice. First to actress and musician Deborah Falconer, from whom he split in the early 2000s, and next to current wife Susan Downey, whom he wed in 2005. He has three children from the two marriages: son Indio, 21, son Exton, 3, and daughter Avri, 5 months.