Simionescu won the French Junior Championships in 1974. She played on the WTA Tour from 1973 to 1980. Her best Grand Slam performance was reaching the 4th round at Wimbledon in 1977. She won 2 singles titles and 1 doubles title. She reached a career-high singles ranking of World No. 36 in 1978.
Simionescu married Björn Borg in 1980, but the marriage ended in 1984. She never remarried, but lived together with the former F1 racer J.-L. Schlesser for a few years, with whom she has a son (Anthony).