Jeri Lynn Zimmermann in Munich, West Germany, the daughter of Gerhard Florian "Jerry" Zimmermann, a Master Sergeant in the United States Army, and his wife Sharon, a social worker. She has one older brother, Mark. As a military brat, Ryan grew up on Army posts in Kansas, Maryland, Hawaii, Georgia, and Texas. When she was eleven, her father retired from the Army and the family settled in Paducah, Kentucky. She graduated from Lone Oak High School in 1986 (as a National Merit Scholar), and then attended Northwestern University, where she was a member of the Alpha Phi sorority.

In 1989, Ryan was chosen Miss Illinois. She was the third runner-up in the 1990 Miss America Pageant, winning the preliminary swimsuit competition. She graduated from Northwestern in 1990 with a Bachelor of Arts degree in Theatre.

After college, she pursued acting full-time in Los Angeles. She made her acting debut in Who's the Boss? and followed that with guest-starring roles in TV shows like Melrose Place, Matlock, and The Sentinel as well as TV movies such as Co-Ed Call Girl.

Her big break came when she won a regular role as the extraterrestrial investigator Juliet Stuart on the TV show Dark Skies. The show was cancelled after one season, but the role had drawn the attention of the science-fiction community.

In 1997, came her biggest role to date. Ryan was chosen for the role of Seven of Nine, a Borg drone who had been freed from the Borg's collective consciousness, on the science fiction series Star Trek: Voyager. After Voyager ended in 2001, Ryan joined the cast of Boston Public in the role of Veronica Cooke, nicknamed "Ronnie," a frustrated lawyer who quits the bar to become a high-school teacher. The show's producer, David E. Kelley, wrote the role specifically for her. The series ended in 2004.

Ryan has recently appeared in such films as Down With Love. She also appeared as Lydia in the independent film Men Cry Bullets. Ryan then starred in her first film lead, in the indie comedy The Last Man, as the last woman left on Earth. The film was released by Lion's Gate.

She also had a recurring role as Charlotte Morgan on The O.C. in the autumn (U.S. September through December) of 2005 and guest-starred as Courtney Reece on David E. Kelley's Boston Legal in 2006. Ryan then co-starred in the CBS legal drama Shark, as Los Angeles County District Attorney Jessica Devlin alongside series lead James Woods, but she did not return for episodes aired after the WGA strike.

Ryan is currently appearing in ABC's medical-drama Body of Proof.