Pamela Wallace co-wrote her first screenplay in the early 1980s. It was rejected multiple times but was finally purchased by producer Edward S. Feldman. The resulting film, Witness, was released in 1985 and starred Harrison Ford and Kelly McGillis. Wallace received the Academy Award for Best Original Screenplay in 1986 for her work on Witness. The script also won awards from the Mystery Writers of America and the Writers Guild of America. The Writers Guild later named Witness to their list of the Top 101 Greatest Scripts.

In the late 1980s, Wallace collaborated with fellow screenwriter Madeline DiMaggio on a screenplay they called "If The Shoe Fits." This was made into a low-budget movie that barely resembled their script. Wallace was given the opportunity to remove her name from the movie credits, but she chose to keep the credit for her resume despite her dislike of the movie.

By the late 1990s, Wallace was once again writing successful screenplays. She wrote the first segment of the award-winning 1996 HBO movie, If These Walls Could Talk. The following year, Borrowed Hearts became one of the highest-rated CBS movies.

Wallace also adapted one of her own novels, Straight From the Heart into a screenplay for Hallmark Channel. The resulting movie became the highest-rated film for the network in 2003. She also penned the screenplay for the 2006 Hallmark Channel movie Though None Go with Me, starring Cheryl Ladd. She has written several other Hallmark Channel and Lifetime Network movies.

Wallace has written 25 romance novels. These have been published under her own name, as well as the pseudonyms Dianne King and Pamela Simpson. An additional pen name, Pamela Simpson, came about through a collaboration with Carla Simpson, who had previously written eleven historical romance novels under the pseudonym Quinn Taylor Evans. In the early 1990s the pair completed three contemporary romantic suspense novels. The novels were translated into seven languages. Two of them, Fortune's Child and Partners in Time, were optioned for film.

In 2000, Wallace wrote a nonfiction book called You Can Write a Screenplay. Drawing on her own experiences in Hollywood, the book walked readers through the entire screenwriting process, beginning with the initial idea. It provided tips for writing the screenplay, as well as advice on how to sell the completed work.

She has served as an executive producer for the cable television series "Beyond the Break", as well as for the television movies Last Chance Cafe and A Very Merry Daughter of the Bride.

Fiction

• Dream Lost, Dreams Found
• Love with the Perfect Stranger
• Straight From the Heart

as Pamela Simpson

• Fortune's Child (with Carla Simpson)
• Partners in Time (with Carla Simpson)

Nonfiction

• You Can Write a Screenplay (2000)