Shear earned titles in several beauty contests, including holding the titles of Miss Louisiana USA 1975 for Miss USA and that of Miss Louisiana for both the Miss World and the Miss International pageants. Among her other titles was Queen of the Floral Trail Society. While she sported the latter title, she posed for a picture in Playboy magazine; though she was fully clothed in the photo, the organizers were opposed to her appearance and rescinded her title.

Shear was born in New Orleans, Louisiana. She attended Loyola University, earning a B.A. in Communications. In 1977, after graduating from Loyola University, Shear moved to Los Angeles, California, to pursue a career in Hollywood.

Shear is best known for her role as a host of the USA Network's 1980s and '90s weekend B-movie show, USA Up All Night. From 1991 to 1998, she hosted in-studio and on-location segments that typically aired on Friday nights, replacing Comedian Caroline Schlitt (the Friday night host for the show's first few years). She also occasionally hosted the show with her Saturday counterpart, Gilbert Gottfried, in addition to making cameos on his edition. Her trademark manner of speaking the show's title, by raising her voice an octave when saying the word "Up", became a catch phrase. Shear also briefly hosted a comedy program called Spotlight Cafe on WWOR-TV in Secaucus, NJ, hosted previously by comic Judy Tenuta.

Shear made two subsequent nude appearances in Playboy: First, in their "Funny Girls" pictorial in June 1991, then in her own pictorial titled "Rhonda Is Up All Night" in October 1993.

In 2001, Shear, with her husband Van Fagan, started Shear Enterprises. Shear began designing from her home office in 2003 with three employees, and launched the Rhonda Shear Intimates line at HSN. Her products were picked up on shopping networks around the world, including The Shopping Channel (Canada) and Ideal World Shopping (U.K.). Rhonda Shear Intimates has continued to grow and is now represented in over 40 countries with over 25 employees in her St. Petersburg, Florida offices.

In 2010, Shear designed the Ahh Bra, and the product was an overnight success. The Ahh Bra was the number-one selling bra worldwide with over 25 million sold internationally. In 2011 the company had 72 million dollars in sales. As of 2013, she has added cosmetics, swim wear, fragrance, and Boomer Hottie.

In 2011, Shear was the event chair and a sponsor for American Cancer Society's Making Strides: Put on Your Pink Bra Event. Between speaking engagements, creating a giant flying bra for the Red Bull Flugtag, and helping with fundraising events, Shear got the chance to meet with women struggling in treatment or following surgery who needed bras that were affordable, feminine, and comfortable. She was struck by their stories, strength, and sense of community. Shear stays connected by donating product every month to women's shelters around the country and continuing her work nationwide with various charitable organizations that fund research and empower women.

In 2014 a line of "intimates, athleisure and loungewear" was announced that was co-designed with Crystal Hefner, 2009 Playboy Playmate and wife of Hugh Hefner, to be sold through Hefner's website.

Shear has written a book titled Up All Night: From Hollywood Bombshell to Lingerie Mogul, Life Lessons from an Accidental Feminist, released in October 2017.