Ferdin played the Bumsteads' daughter Cookie in the 1968–1969 CBS revival series Blondie.
She was subsequently cast Felix Unger's daughter Edna in the 1970s ABC series version of The Odd Couple and Paul Lynde's daughter Sally on the short-lived The Paul Lynde Show.

She appeared on Star Trek in 1968 as one of a group of orphaned children led by an alien with sinister motives in the episode "And the Children Shall Lead" and in the 1977 series Space Academy as Laura Gentry.

Ferdin's distinctive voice soon secured her voice roles, and she was cast to provide the voice of Lucy van Pelt in three Peanuts cartoons: the 1969 TV special It Was a Short Summer, Charlie Brown, a 1969 feature film A Boy Named Charlie Brown and the 1971 TV special Play It Again, Charlie Brown.
Ferdin was a frequent guest star on episodic television in the 1960s and 1970s, with appearances on Bewitched, Green Acres, The Andy Griffith Show, Branded, Daniel Boone, Custer, The Monkees, The Flying Nun, The Second Hundred Years, Gunsmoke,  Shazam!,
The High Chaparral, Mannix, The Brady Bunch, Family Affair, Love, American Style, Marcus Welby, M.D., Sigmund and the Sea Monsters, Apple's Way, The Streets of San Francisco, Baretta, CHiPS, and 240-Robert.

She had a brief and uncredited role in The Reluctant Astronaut (1967) and was featured in the Walt Disney musical The One and Only, Genuine, Original Family Band (1968).
She appeared as Mary Constable in the supernatural thriller Daughter of the Mind and as Abby Clarkson in the horror film The Mephisto Waltz (1971) with Alan Alda.
The same year, Ferdin appeared in The Christine Jorgensen Story, based on the life of the first trans woman in the United States to undergo sex reassignment surgery, and in The Beguiled alongside Clint Eastwood and Geraldine Page.
She then appeared in the Kurt Vonnegut adaptation Happy Birthday Wanda June, and in the exploitation horror film The Toolbox Murders (1978).

She voiced Fern Arable, the little girl who raises Wilbur the pig, in the 1973 animated film Charlotte's Web.

Ferdin was considered for the role of Regan MacNeil, the demon-possessed girl in the 1973 William Friedkin film The Exorcist, but casting directors decided she was too well-known and cast the less familiar actress Linda Blair.

She withdrew from acting in the mid-1980s, but did voice the character of Shelley Kelley in the Kids' WB series Detention in 1999.

In January 2020, Pamelyn became the co-host of the television entertainment talk show, "Ken Boxer Live," on TVSB TV originating in Santa Barbara, California with host Ken Boxer.
Ferdin played the Bumsteads' daughter Cookie in the 1968–1969 CBS revival series Blondie. She was subsequently cast Felix Unger's daughter Edna in the 1970s ABC series version of The Odd Couple and Paul Lynde's daughter Sally on the short-lived The Paul Lynde Show.
She appeared on Star Trek in 1968 as one of a group of orphaned children led by an alien with sinister motives in the episode "And the Children Shall Lead" and in the 1977 series Space Academy as Laura Gentry.
Ferdin's distinctive voice soon secured her voice roles, and she was cast to provide the voice of Lucy van Pelt in three Peanuts cartoons: the 1969 TV special It Was a Short Summer, Charlie Brown, a 1969 feature film A Boy Named Charlie Brown and the 1971 TV special Play It Again, Charlie Brown. Ferdin was a frequent guest star on episodic television in the 1960s and 1970s, with appearances on Bewitched, Green Acres, The Andy Griffith Show, Branded, Daniel Boone, Custer, The Monkees, The Flying Nun, The Second Hundred Years, Gunsmoke,  Shazam!, The High Chaparral, Mannix, The Brady Bunch, Family Affair, Love, American Style, Marcus Welby, M.D., Sigmund and the Sea Monsters, Apple's Way, The Streets of San Francisco, Baretta, CHiPS, and 240-Robert.
She had a brief and uncredited role in The Reluctant Astronaut (1967) and was featured in the Walt Disney musical The One and Only, Genuine, Original Family Band (1968). She appeared as Mary Constable in the supernatural thriller Daughter of the Mind and as Abby Clarkson in the horror film The Mephisto Waltz (1971) with Alan Alda. The same year, Ferdin appeared in The Christine Jorgensen Story, based on the life of the first trans woman in the United States to undergo sex reassignment surgery, and in The Beguiled alongside Clint Eastwood and Geraldine Page. She then appeared in the Kurt Vonnegut adaptation Happy Birthday Wanda June, and in the exploitation horror film The Toolbox Murders (1978).
She voiced Fern Arable, the little girl who raises Wilbur the pig, in the 1973 animated film Charlotte's Web.
Ferdin was considered for the role of Regan MacNeil, the demon-possessed girl in the 1973 William Friedkin film The Exorcist, but casting directors decided she was too well-known and cast the less familiar actress Linda Blair.
She withdrew from acting in the mid-1980s, but did voice the character of Shelley Kelley in the Kids' WB series Detention in 1999.
In January 2020, Pamelyn became the co-host of the television entertainment talk show, "Ken Boxer Live," on TVSB TV originating in Santa Barbara, California with host Ken Boxer.
Pamelyn Ferdin