Favourite Kirani James won the men's 400m event at this afternoon's Diamond League meeting in Birmingham.
"I'm very pleased with that," James told reporters. "I've had a successful end to the season, it's always good to finish on a high."
Rooney added: "I had tired legs and it's been a really busy week after the Euros. I've won my first ever Diamond League points today at 27 years old.
"Third is good but I would have liked to have run faster but I can't complain after a great season."
Rooney's fellow Brit Matthew Hudson-Smith (46.60s) was seventh.