Mimi was born in New York City in 1952; the daughter of Etyl, a classical pianist, and Paul Leder, a director, producer, actor, writer, and editor. Mimi was raised in Los Angeles, in a Jewish home. During childhood, her dad, a low-budget indie filmmaker, introduced Mimi and her siblings to film production. Having worked for the majority of her life in film gave her the skill and confidence to be the first woman accepted into the American Film Institute. She studied cinematography but enjoyed working with actors and telling stories.
Mimi began her career as a script supervisor on a string of films, including Spawn of the Slithis, Dummy, The Boy Who Drank Too Much, and A Long Way Home, before moving on to the TV series Hill Street Blues. After making a short film, Short Order Dreams, written and funded by her father Paul, she screened it for Steven Bochco, creater of Hill Street Blues, and his friend Gregory Hoblit who hired her to direct an episode of L.A. Law.
In 1988 Mimi went on to direct episodes of Crime Story, The Bronx Zoo, Midnight Caller, before getting hired to direct several episodes of China Beach for which she was nominated for four Emmys. She decided to make a few made-for-TV films, Woman with a Past, House of Secrets, and Baby Brokers before getting hired as one of the core directors for ER. She made proficient use of her cinematography background and the steadicam to create high energy scenes that moved around the corridors and rooms of the hospital. The show earned her Emmy Awards for Outstanding Drama Series in 1995 and 1996. She returned to direct an episode of the series during its final season in 2009. She was receiving much attention and soon received a job offer from Steven Spielberg as a director of the film The Peacemaker, an action-adventure film that she insists she sees a drama. Mimi becaem one of only a handful of woman directors to break into the action genre, and her assignment to this film generated much press about the opportunities for women directors in Hollywood. She studied trains and other visual effects to prepare herself for the film and is proud of the results.
Continuing to work for DreamWorks, she directed Deep Impact and Pay It Forward while simultaneously creating a personal love story about her parents, Sentimental Journey. Since then, Mimi has been moving back and forth between television and film, executive producing and directing such television series as The Beast, John Doe, Johnny Zero, Vanished, and Shameless, and films or made-for-TV films such as Thick as Thieves', U.S. Attorney, and Heavenly.
In 2011, she was named as director for a proposed remake of the film All Quiet on the Western Front.
Mimi has one daughter, Hannah, with her husband Gary Werntz.