A contralto, she is best known as one-half of the 1970s duo Captain & Tennille with her former husband Daryl Dragon; their signature song is "Love Will Keep Us Together".

For five years, her mother, also named Cathryn (née Wright), hosted a daily television show in Montgomery.

In 1959, after her father's furniture store failed, Tennille's family moved from Montgomery to Balboa, California, where she worked first as a file clerk and then as a statistical analyst for North American Rockwell Corporation.

[4]: 2 While living in Corona del Mar in Newport Beach, California, during the late 1960s, Tennille was a member of the South Coast Repertory.

The musical was a success locally, went on the road to San Francisco and Los Angeles in 1971, and eventually made it to Broadway for a few dates at the Belasco Theatre in October 1972.

[11] In 1975, the title track from the duo's debut studio album, Love Will Keep Us Together topped the Billboard pop chart for four weeks starting June 21, 1975.

Following the success of "Love Will Keep Us Together", A&M re-released the Tennille-penned "The Way I Want to Touch You" in September 1975, with the song becoming the duo's second #1 hit on the Adult Contemporary charts of both the US and Canada.

During the duo's period of highest popularity, Tennille also worked as a session singer (most frequently partnered with the Beach Boys' Bruce Johnston), performing as a backing vocalist on the Elton John albums Caribou,[5] Blue Moves, and 21 at 33 (some vocally arranged by Dragon) and most notably on the hit track "Don't Let the Sun Go Down on Me".

On July 8, 1980, Tennille sang the national anthem at the Major League Baseball All-Star game at Dodger Stadium in Los Angeles.

From September 1998 to June 1999, Tennille starred in the lead role of Victoria Grant/Count Victor Grazinski in the national tour of the Broadway musical Victor/Victoria.

[23] In November 2003, Tennille performed a benefit concert for the Reno, Nevada Chamber Orchestra, where her surprise guest was Dragon.

[28] During the promotion of her autobiography on The Today Show in the spring of 2016, Tennille said the reason for their divorce was Dragon's "inability to be affectionate.

[31] Dragon stated in a February 2017 interview with People that Tennille had returned to Arizona to assist him following a serious health-related incident he had experienced the previous year.