Myrna Adele Williams was born in Radersburg, Montana on 02 August, 1905. Myrna was named for a train station her father once passed through. Her parents were David Williams, a rancher of Welsh descent, and Adelle Johnson. Her father was also a banker and real estate developer, who, at age 21, was the youngest man ever elected to the Montana state legislature. Her mother studied music at the American Conservatory of Music in Chicago, and was a talented pianist.

Loy made her stage debut at age 12, performing a dance she choreographed herself based on "The Blue Bird" from the Rose Dream Operetta, at Helena's Marlow Theater. At age 13, her father died and Loy moved with her family to Los Angeles, California. There she began appearing in local stage productions at age 15, while attending Venice High School. Also while attending Venice High, in 1921, she posed for a statue which stood in front of the school until constant vandalism and decay led to its removal in the early 21st century.

Eventually, Loy was discovered by Rudolph Valentino and his wife, Natacha Rambova. After failing several screen tests, she landed a bit part in What Price Beauty?, which was written by Rambova. She spent the next several years playing bit parts, largely vamps and often exotic - Asian or Latin beauties. Loy successfully weathered the transition to sound films (appearing in some of the earliest, including The Jazz Singer [1927]), and received better supporting roles by the early 1930s.

She appeared in early technicolor musicals, including The Show of Shows (1929), Under a Texas Moon (1930), and The Bride of the Regiment (1930). She played an increasing number of lead roles in the early 1930s, including Vanity Fair (1932), The Barbarian (1933), with Ramon Novarro, and The Prizefighter and the Lady (1933) with boxer Max Baer.

1934 proved to be an eventful year for Loy. She starred in Manhattan Melodrama with Clark Gable and William Powell. The film became infamous when gangster came out of hiding to see it, reportedly because of Loy's appearance in it, and was shot to death upon leaving the theater. Also in 1934, Loy landed the role that destined her superstardom. Director W.S. Van Dyke detected an untapped wit and sense of humor in the actress, and to test her reaction, pushed her into a swimming pool at a party. Satisfied with the aplomb with which she reacted, Van Dyke offered her the role of Nora Charles, opposite William Powell in The Thin Man.

The film was enormously successful, largely due to Powell and Loy's outstanding chemistry and sparkling wit. She and Powell would appear in a total of fourteen films together, becoming the most prolific pair in Hollywood history. Loy's performances as Nora Charles led to her often being labelled "The Perfect Wife." James Stewart joked that "There ought to be a law against any man who doesn't want to marry Myrna Loy," and Men-Must-Marry-Myrna clubs sprang up across the country. Her success in Manhattan Melodrama and The Thin Man led to a number of important films in the ensuing years, such as Wife vs. Secretary (1936) with Clark Gable and Jean Harlow.

She then made several movies with Powell in quick succession. These included The Great Ziegfeld (1936), playing Billie Burke to Powell's Florenz Ziegfeld; Libeled Lady (1936), which also starred Jean Harlow and Spencer Tracy; After the Thin Man (1936), the second in the series of six; and Double Wedding (1937), a romantic comedy of the sort for which Loy had become well known. She also made three more films with Clark Gable in 1937 and 1938: Parnell (1937), the worst-recieved film of either Loy's or Gable's career, Test Pilot (1938), and Too Hot To Handle (1938).

By the late 1930s, Loy was one of the most succesful actresses in Hollywood. She appeared on the annual Quigley Poll of the Top Ten Money Making Stars in both 1937 and 1938, and in 1938 was crowned Queen of Hollywood in a poll, which named Clark Gable as King. Having grown famous as a comedic performer, Loy demonstrated her dramatic ability in The Rains Came (1939), opposite Tyrone Power. Before the outbreak of World War II, Loy completed several more comedies, including Third Finger, Left Hand (1940) with Mervyn Douglas, and Another Thin Man (1939), I Love You Again (1940), Love Crazy (1941), and Shadow of the Thin Man (1941), all with William Powell.

With the onset of World War II, Loy virtually abandoned her acting career in favor of assisting with the war effort. She donned a uniform when she joined the Hollywood chapter of "Bundles for Bluejackets." Loy helped run a Naval Auxiliary Canteen and made frequent fundraising tours. She was so outspoken against Adolph Hitler that her name appeared on his blacklist. During the war she made only one film, The Thin Man Goes Home (1944).

Following the war, Loy returned to acting with what she considered to be her greatest acting achievement. She played the supportive wife of a returning serviceman (Fredric March) in The Best Years of Our Lives (1946).

In the later 1940s, Loy starred with Cary Grant in the comedies The Bachelor and the Bobby-Soxer (1947) and Mr. Blandings Builds His Dream House (1948). Her film career in the 1950s was sparse, though it included most notably Cheaper By the Dozen (1950) and its sequel, Belles On Their Toes (1952). Through the early 1980s, she appeared sporadically on television shows and in made-for-TV movies, and made her Broadway debut in a revival of Clare Booth Luce's The Women in 1973.

Loy survived breast cancer in the 1970s, undergoing two mastectomies in 1975 and 1979. On 14 December, 1993, while undergoing unspecified surgery in New York City, she died at age 88. She was buried in Helena, Montana, where the Myrna Loy Center for the Performing Arts operates in the historic Lewis and Clark County Jail building.

Loy had no children, though she married four times. Her turbulent romantic life posed an ironic contrast to her frequent screen persona as "The Perfect Wife." She joked, "Some perfect wife I am. I've been married four times, divorced four times, have no children, and can't boil an egg."

Throughout her life, Loy remained active in a number of political causes. She campaigned for better parts and equal rights for black actors, and was the first Hollywood celebrity to become a member of the US National Commission for UNESCO, which she joined in 1948. In 1987, Loy's autobiography, Myrna Loy: Being and Becoming, was published.

Though Loy was never even nominated for an Academy Award for a performance, she received an Academy Honorary Award in 1991 "for her career achievement," after much lobbying by her supporters and acquaintances. She accepted via camera from her Manhattan apartment, saying only "You've made me very happy. Thank you very much." It was her last public appearance.

Loy's film roles spanned from the era of silent films through two decades of active performing. By the late 1940s, her career had slowed down, but nonetheless, throughout her career, Loy appeared in a remarkable 129 films, including many now regarded as classics.