Plumb played Jan from 1969 until 1974. Seeking other parts and perhaps hoping to distance herself from strong identification as "Jan", she did not rejoin her television siblings for the later Brady Bunch Variety Show. During production of the show, Plumb appeared in NBC productions of Little Women, in both TV Movie and a short-lived Series format.

In 1976, she surprised everyone with a stunning dramatic performance in the made-for-television movie Dawn: Portrait of a Teenage Runaway, and joined the LA based Groundlings Improv comedy troupe. In the late 1970s Plumb chose to participate in the Brady made-for-TV movies that followed, including The Brady Girls Get Married which gave her a featured role, and The Brady Brides, a sitcom in which she was a co-lead. She also appeared in later Brady movies and series as well, including "A Very Brady Christmas" and "The Bradys".

Plumb appeared steadily on stage and in television roles through the 90's, in roles both small and large. She appeared in the Saturday morning sitcom Fudge (1995-1997) as Fudge's mother, Mrs. Ann Thatcher and in the movie Fudge-A-Mania (1997). In addition, Plumb had a very memorable cameo appearance in the 1988 movie I'm Gonna Git You Sucka.

Of all the Brady Bunch child cast, Plumb has worked most consistently to carve an acting career distanced from her role on the show. This has apparently lead to conflicting feelings about the Brady Bunch. In an article published by the Chicago Tribune in the 1990s on The Real Live Brady Bunch, Plumb participated in a performance (albeit not as "Jan") and was met by enthusiastic fans who asked "What was your favorite episode?", to which she replied "The last one." Seeing their disappointment, she modifed her answer by saying "The Grand Canyon episode was kind of cool."

In a VH1 special, "The Brady Bunch 35th Anniversary Reunion Special: Still Brady after All These Years", broadcast on September 29, 2004, Plumb stated that she had never seen the "Brady Bunch Movie", and was notably somewhat understated and thoughtful during the light-hearted special. When asked to give the audience an update as to her life today, she stated that she was "still auditioning".

Plumb currently resides in Laguna Beach, California with her husband Kenneth Pace (1995-present). She is also an artist, and has been a member of the Laguna Beach Board of Adjustments/Design Review Board since February 2002. She was elected chair pro-tem of that board in February 2005.