In 1953, she signed with the Indianapolis Clowns where she became the first female pitcher in the league. Being one of few females playing the league, she attracted a lot of fans and followed through with the hype by showing great skill and courage.
According to A Strong Right Arm: The Story of Mamie "Peanut" Johnson by Michelle Y. Green, by the end of her career in 1955, she had a 33–8 record.
During an interview with NPR in 2003, Johnson commented, “I met some of the nicest gentlemen I could ever meet and I got the highest respect in the world from all of them.” However, she added, “You’ve got your gentlemen, and then you’ve got your men.” Some of the “men” didn’t know how to act, she says, “but after you prove yourself as to what you came there for, then you don’t have any problem out of them, either. After you strike three or four of them out... you know, it’s alright.”
After her short-lived baseball career, she went on to obtain a nursing degree from North Carolina A&T State University and worked as a nurse for 30 years at Sibley Memorial Hospital in Washington, DC.
She later operated a Negro-leagues memorabilia shop in Capitol Heights, Maryland.
Sadly, she passed away on December 19, 2017, at the age of 82.