Mowry and her sister began entering pageants and talent shows while their family was stationed at Fort Hood, Texas. At age 12, they convinced their mother to move to California with them so they could pursue acting. She agreed, on the condition that they land an acting job within the first month of their stay. In 1990, their family moved to California permanently, settling in Los Angeles, and she and her sister began appearing in commercials and small roles.

After the show ended, both Mowry and her sister studied psychology at Pepperdine University. She also went to Europe to study humanities and Italian for a period. Both she and her sister appeared in the Rob Schneider comedy film The Hot Chick, playing cheerleaders. Mowry also did voiceovers for the Bratz cartoon series as the voice of Sasha. In 2005, Mowry and her sister both starred in the Disney Channel Original Movie Twitches and reprised their roles in its sequel, Twitches Too and before co-starred in the 2000 movie Seventeen Again. Tia also appeared on an episode of her sister's television show, Strong Medicine, in January 2006, playing the role of Keisha, the twin sister of Tamera Mowry's character, Dr. Kayla Thornton. Mowry has a starring role in the BET television series The Game as Melanie Barnett. Mowry has been nominated for a Teen Choice Award and a NAACP Image Awards for best Actress in a comedy.

Mowry met actor Cory Hardrict on the set of their movie, Hollywood Horror. They dated for six years, then became engaged on Christmas Day, 2006, and married in California on April 20, 2008. On January 11, 2011, People announced that Mowry and Hardrict were expecting their first child; Mowry made the announcement herself on 106 & Park. The pregnancy was documented on the show Tia & Tamera featuring her sister, Tamera Mowry, on the Style Network. The couple welcomed a son, Cree Taylor Hardrict, on June 28, 2011. On November 8, 2017, Mowry announced that she was pregnant with her second child, a girl.

In the Blue's Clues episode "Blue's Birthday", Mowry and her sister make a cameo appearance as two of the celebrities wishing Blue a happy birthday. Their only line is said in unison: "Happy Birthday, Blue!" Beginning in July 2011, the Style Network began airing Tia & Tamera, a reality show which follows the day-to-day lives of the twins; Tia being pregnant and Tamera planning her wedding. Mowry and her sister are both Singers. They have showcased their vocal abilities on episodes of Sister Sister, including covers of "You Can't Hurry Love", "Amazing Grace" and "I'm Going Down", which Tamera performed. They also sang the theme song during season five and six.

In May 2012, Mowry published her first book, Oh, Baby: Pregnancy Tales and Advice from One Hot Mama to Another, about her pregnancy and being a working mother. In May 2012, Mowry stated via her Twitter account that she would not be returning to The Game, for a sixth season. In August 2013 it was announced that she was cast in the lead role in a new Nickelodeon comedy series Instant Mom alongside Michael Boatman and Sheryl Lee Ralph.

Since 2015, Mowry has starred in her Cooking Channel series Tia Mowry at Home where she makes everything from macaroni and cheese, cake, pie, curry chicken, collard greens, shakshuka, potato, galette and various types of cocktails. Some of her guest stars have included her Game co-stars Pooch Hall, Hosea Sanchez, Wendy Raquel Robinson, Brittany Daniel, Lilly Singh from YouTube and Kelly Rowland from Destiny's Child. In 2016, Mowry started a podcast on PodcastOne called Mostly Mom with Tia Mowry. On April 29, 2016, she appeared with her twin sister on the daytime talk show The Real, where she promoted her new book Twintution.