Born in Nevada, Pat Ryan grew up in Los Angeles, California. She graduated from high school in 1929, then attended Fullerton Junior College and later the University of Southern California. She paid for her schooling by working multiple jobs, including pharmacy manager, typist, X-ray technician, and retail store clerk. In 1940, she married lawyer Richard Nixon; they had two daughters. Pat campaigned for her husband in his successful congressional campaigns of 1946 and 1948. Richard Nixon was elected Vice President in the Eisenhower administration, whereupon Pat undertook many missions of goodwill with her husband and gained favorable media coverage. She assisted her husband in both his unsuccessful 1960 presidential campaign, and later in his successful presidential campaign of 1968.

As First Lady, Pat Nixon promoted a number of charitable causes, including volunteerism. She oversaw the collection of more than 600 pieces of historic art and furnishings for the White House, an acquisition larger than that of any other administration. Pat became the most traveled First Lady in U.S. history up to that time, visiting about 80 nations; she was the first First Lady to enter a combat zone. These trips gained her favorable reception in the media and the host countries. Her tenure ended when, after being re-elected in a landslide victory in 1972, President Nixon resigned two years later amid the Watergate scandal.

Her public appearances became less frequent in her later life. She and her husband returned to California, and later moved to New Jersey. Pat suffered two strokes—one in 1976 and another in 1983—and was later diagnosed with lung cancer in the early 1990s. She died in 1993 aged 81.

Thelma Catherine Ryan was born in the small mining town of Ely, Nevada, the day before St. Patrick's Day. Her father, William M. Ryan, Sr., was a sailor, gold miner, and truck farmer of Irish descent. Her mother, Katherine Halberstadt, was a German immigrant.

Pat was a nickname given to her by her father, referring to her birthdate and Irish ancestry. Upon enrolling in college in 1931 she dropped her first name of Thelma, replacing it with Pat and occasionally rendering it as Patricia; the name change, however, was not a legal action, merely one of preference.

After her birth, the Ryan family moved near Los Angeles, California, and in 1914 settled on a small truck farm in Artesia (present-day Cerritos). During this time she worked on the family farm, and also at a local bank as a janitor and bookkeeper. Her mother died of cancer in 1924. Pat, who was 12 at the time, assumed all the household duties for her father, who died in 1929 of silicosis, and two older brothers, William Jr. (1910–1997) and Thomas (1911–1992). She also had a half-sister, Neva Bender (born 1909), and a half-brother, Matthew Bender (born 1907), from her mother's first marriage; her mother's first husband had died during a flash flood in South Dakota.

It has been said that few, if any, First Ladies worked as consistently before their marriage as did Pat Nixon. As she told the writer Gloria Steinem during the 1968 presidential campaign, "I never had time to think about things like that—who I wanted to be, or who I admired, or to have ideas. I never had time to dream about being anyone else. I had to work."

After graduating from Excelsior High School in 1929, Pat Ryan attended Fullerton Junior College. She paid for her education by working odd jobs, including as a driver, a pharmacy manager, a telephone operator, and a typist. She also earned money sweeping the floors of a local bank, and from 1930 until 1932, she lived in New York City, working as a secretary and an X-ray technician.

Determined "to make something out of myself", she enrolled in 1931 at the University of Southern California (USC), where she majored in merchandising. As a former professor noted, "She stood out from the empty-headed, overdressed little sorority girls of that era like a good piece of literature on a shelf of cheap paperbacks." The young Ryan held part-time jobs on campus, worked as a sales clerk in Bullock's-Wilshire department store, taught typing and shorthand at a high school, and supplemented her income by working as an extra in the film industry. She appeared as part of a brief walk-on in the 1935 film Becky Sharp, as well as the 1936 film The Great Ziegfeld.

In 1937, Pat Ryan graduated cum laude from USC with a Bachelor of Science degree in merchandising, together with a certificate to teach at the high school level, which USC deemed equivalent to a Master's degree. Pat accepted a position as a high school teacher in Whittier, California.