Pendleton died of a heart attack in Fresno, California on Sunday, reports variety.com.
She appeared on the classic children's television series from 1955 to 1959, making her one of only nine children that appeared on the show for its entire run.
One of the youngest of the Mouseketeers, she was best known for her shoulder-length blond curls and frequently being paired with fellow Mouseketeer Cubby O'Brien for the "Mickey Mouse Club" end of show song.
Pendleton was born in Glendale, Califorina, in 1946, the youngest of three children.
She was recruited to audition for "Mickey Mouse Club" when Disney producers visited dance schools in the Los Angeles area in search of child talent.
After her time as a Mouseketeer, Pendleton left show business.
In 1983, Pendleton became paralyzed from the waist down due to an automobile accident. She spent the rest of her life in a wheelchair.
Post accident, Pendleton returned to school, eventually earning a Bachelor's and Master's degree in Psychology. She worked at a shelter for battered women and served on the board for the California Association of the Physically Handicapped.
Pendleton maintained her longtime friendships with fellow Mouseketeers over the years.
She frequently appeared with them in "Mickey Mouse Club" reunion shows and parades at Disneyland.
"My mom loved her Mouseketeer family. Getting together with them was always a high point. It gave her the opportunity to relive great memories and to meet so many 'Mickey Mouse Club' fans that watched the show as kids and loved her. Many told her that they named their daughters 'Karen' in her honour," her daughter said in a statement.
Pendleton is survived by her daughter, Staci Bletscher, and two grandchildren.
( With inputs from IANS )