Henry was born as Gloria Eileen McEniry on April 2, 1923. She lived and grew up on the edge of the Garden District of New Orleans, Louisiana. She was educated at the Worcester Art Museum School in Massachusetts. She moved to Los Angeles in her late teens and worked on a number of radio shows and commercials using the stage name of Gloria Henry. Her topics of discussions were gossip, fashion, and sports. She also performed in little theater groups.

Signed by an agent, Henry transitioned into film work via Columbia Studios in 1946, and made her debut as the female lead in the horse racing film Sport of Kings (1947). She had featured roles in the romantic comedy Miss Grant Takes Richmond (1949) that starred Lucille Ball, and the western Rancho Notorious (1952) with Marlene Dietrich. Henry also appeared in three sports-themed stories;, the football film Triple Threat (1948), the horse race tale Racing Luck (1948), and the William Bendix baseball comedy Kill the Umpire (1950).

Henry is of Scottish and Irish ancestry. She was married to Robert D. Lamb between 1943 and 1948. She wed architect Craig Ellwood in 1949; they divorced in 1977. The couple had three children, Jeffrey, Adam, and Erin Ellwood.

In 1959, Henry landed the role for which she would become most well-known, that of Dennis’ mother “Alice Mitchell” on the CBS comedy television series Dennis the Menace. The series co-starred Herbert Anderson as her husband, and young Jay North in the title role of Dennis. Henry portrayed sunny domesticity and maternal warmth for four seasons until the series’ cancellation in 1963.

Henry’s career slowed down considerably after Dennis the Menace. In 1992, she stated that she had become so associated with the role of Alice Mitchell that she had become typecast in mother roles. She appeared occasionally in TV movies playing assorted bit-part matrons, and in 1989, she played a small role as an art-collecting society matron in the prime time soap opera Dallas.

Henry returned to the big screen in a brief role in Her Minor Thing (2005), a romantic comedy directed by Charles Matthau, Walter Matthau’s son. She occasionally attended film festivals and nostalgia conventions. In 2012, she guest-starred on the Parks and Recreation episode “Campaign Shake-Up”, playing the role of Mary-Elizabeth Clinch.