Born in Isleton, California to Japanese immigrants, the son of an itinerant fruit worker, Morita developed spinal tuberculosis at age two and spent the bulk of the next nine years in Northern California hospitals, including the Shriners Hospital in San Francisco. He was for long periods wrapped in a full body cast and was told he would never walk. Often alone and isolated, young Morita made sock puppets to entertain himself.

After a surgeon fused four vertebrae in his spine, Noriyuki finally learned to walk again at age 11. By then, his Japanese American family had been sent to an internment camp to be detained for the duration of World War II. He was transported from the hospital directly to the Gila River camp in Arizona to join them. It was at this time that he met a Catholic priest from whom he would later take his stagename "Pat".

For a time after the war, the family operated Ariake Chop Suey, a restaurant in Sacramento, California. Teenage "Nori" would entertain customers with jokes and serve as master of ceremonies for group dinners.

Noriyuki graduated from Armijo High School in Fairfield, California and shortly thereafter moved back to the Sacramento area, where he took a job with Aerojet-General, an aerospace company that designed and manufactured rocket engines, including those for the US Navy's UGM-27 Polaris.

It was only after working his way up to head of a computer operations department that Morita, by now a husband and father, and also seriously overweight, decided he had taken the wrong path in life. He quit and became a standup comedian. Often billed as "the Hip Nip" in his standup act, he became a member of the Los Angeles improvisational comedy troupe The Groundlings.

His first movie role was as a stereotypical henchman in Thoroughly Modern Millie (1967). Later, a recurring role as a Korean Captain Sam Pak on the sitcom M*A*S*H helped advance the comedian's acting career.

He had a recurring role on the show Happy Days as Mesuma "Arnold" Takahashi, owner of the diner Arnold's. After the first season (1975-1976), he left "Happy Days" to star as inventor Taro Takahashi in his own show, Mr. T and Tina, the first Asian American sitcom on network TV. The sitcom was placed on Saturday nights by ABC and was quickly cancelled after a month in the fall of 1976. In 1977 Morita starred in the short lived Blansky's Beauties as "Arnold". Morita eventually returned to Happy Days, reprising his role in the 1982-1983 season. He appeared in an episode of The Odd Couple, and also had a recurring role on the NBC sitcom Sanford and Son in the mid-1970s, playing a Japanese chef named Ah Chew.

Morita gained worldwide fame playing wise karate teacher Keisuke Miyagi who taught young "Daniel-san" (Ralph Macchio) in The Karate Kid, a film that included the famous quote "Wax on, wax off" and also taught young "Julie-san" (Hillary Swank) in The Next Karate Kid. He was nominated for an Academy Award for Best Supporting Actor as well as a Golden Globe and reprised his role as the sensei Mr. Miyagi in three sequels. Morita never formally practiced a martial art and most of his karate scenes were performed by stunt double (and noted shito-ryu karate-ka) Fumio Demura. Although he had been using the name "Pat Morita" for years, producer Jerry Weintraub suggested that Pat be billed with his given name to sound more ethnic (see ).

Morita went on to star as the title character in the ABC detective show Ohara which aired in 1987 and ended a year later due to poor ratings. He then wrote and starred in the World War II romance film Captive Hearts (1987).

Late in his career, Morita starred on the Nickelodeon television series The Mystery Files of Shelby Woo and a recurring role on the sitcom The Hughleys. He also starred in the short film, Talk To Taka, somewhat reprising his role of Arnold, as a Sushi Chef that doles out advice to anyone that will hear him.

Morita also had a cameo appearance in the 2001 Alien Ant Farm music video "Movies." Morita's appearance in the video spoofed his role in The Karate Kid.

He would also reprise his role (to an extent) in the stop-motion animated series Robot Chicken. In the episode, he is assumed to be Mr. Miyagi, but he immediately denies that by saying, "First of all, I'm Pat F'in Morita, ya nutsack!" He trains Joey Fatone how to do karate in order to defeat the Yakuza thugs that killed the other 'N Sync members.

One of Morita's last TV roles was as Master Udon on the SpongeBob SquarePants episode, Karate Island. The episode was dedicated to him after he died about six months after the episode's first run. One of his last film roles was in the 2005 independent feature film, Only the Brave, about the 442nd Regimental Combat Team, where he plays the father of lead actor (and director) Lane Nishikawa.

Like many Asian American actors, Morita spoke English with a natural American accent[specify] but was frequently typecast with a Japanese or Korean accent.

Morita died on Thanksgiving Day, November 24, 2005 in Las Vegas, Nevada, at age 73. According to an article in People Magazine, Evelyn Guerrero, his third wife (separated from Morita by the time of his death), attributed the cause of his death to complications associated with alcoholism. This makes Morita the third Kingdom Hearts cast member to pass away, the other two being Tony Pope (Gepetto in Kingdom Hearts) and John Fiedler (Piglet in Kingdom Hearts)

He is survived by his daughters, Erin, Aly and Tia, and two grandchildren.

Among his last roles was a voicework in the videogame Kingdom Hearts II, in which he reprised his role as the Chinese Emperor from Mulan. He also appeared in an episode of SpongeBob SquarePants (Karate Island) which wasn't released until after his death; the episode was dedicated to his memory.

His last movie was Royal Kill which also stars Eric Roberts, Gail Kim, and Lalaine and is directed by Babar Ahmed.