Switzer was born in Paris, Illinois, the third son and last of the four children of Gladys C. Shanks and George Frederick Switzer. The oldest brother died in 1922. A sister Janice was born in 1923 and a brother Harold was born in 1925. Of Scottish and German ancestry he was named Carl after a member of the Switzer family and Dean after many relatives on his grandmother's side. He and his brother Harold became famous in their hometown for their musical talent and performances. Both sang and could play a number of instruments.

Switzer began his career as a child actor in the mid-1930s appearing in the Our Gang short subjects series as Alfalfa, one of the series' most popular and best-remembered characters. After leaving the series in 1940, Switzer struggled to find substantial roles owing to typecasting. As an adult, he appeared mainly in bit parts and B-movies. He later became a dog breeder and hunting guide.

In 1934, the Switzers traveled to California to visit family. While sightseeing, they went to Hal Roach Studios. Following a public tour, 8-year-old Harold and 6-year-old Carl entered the Hal Roach Studio's open-to-the-public cafeteria, the Our Gang Café, and began an impromptu performance. Producer Hal Roach was present and was impressed. He signed both brothers to appear in Our Gang. Harold was given two nicknames, "Slim" and "Deadpan," while Carl was dubbed "Alfalfa."

The brothers first appeared in the 1935 Our Gang short Beginner's Luck. By the end of the year, Alfalfa was one of the main characters, while Harold had been relegated to the background. Although Carl was an experienced singer and musician, his character Alfalfa was often called upon to sing off-key renditions of popular songs, most often those of Bing Crosby. Alfalfa also sported a cowlick.

By the end of 1937, Alfalfa had surpassed George "Spanky" McFarland, the series' nominal star, in popularity. While the boys got along, their fathers argued constantly over their sons' screen time and salaries. Switzer's best friend among the Our Gang actors was Tommy Bond, who played his on-screen nemesis "Butch." In Bond's words, he and Switzer became good friends because "neither of us could replace the other since we played opposites." However, Switzer was known for being abrasive and difficult on the set. He would often play cruel jokes on the other actors and hold up filming with his antics.

Switzer's tenure on Our Gang ended in 1940, when he was twelve. His first role after leaving the series was as co-star in the 1941 comedy Reg'lar Fellers. The next year, he had a supporting role in Mrs. Wiggs of the Cabbage Patch. Switzer continued to appear in films in various supporting roles, including in Johnny Doughboy (1942), Going My Way (1944), and The Great Mike (1944). Switzer had an uncredited role as Auggie in the 1943 film The Human Comedy. Switzer's last starring roles were in a brief series of imitation Bowery Boys movies. He reprised his "Alfalfa" character, complete with comically sour vocals, in PRC's Gas House Kids comedies in 1946 and 1947. By this time Switzer was downplaying his earlier Our Gang work. In his 1946 resume, he referred to the films generically as "M-G-M short product."

Switzer had small parts in both the 1946 Christmas film It's a Wonderful Life as Mary Hatch's (Donna Reed) date at a high school dance in the film's beginning and again in the 1948 film On Our Merry Way as the mayor's son, a trumpet player in a fixed musical talent contest. In the 1954 musical film White Christmas, his photo was used to depict "Freckle-Faced Haynes," an army buddy of lead characters Wallace and Davis (played by Bing Crosby and Danny Kaye) who was also the brother of the female leads the Haynes Sisters (played by Rosemary Clooney and Vera-Ellen).

In the 1950s, Switzer turned to television. Between 1952 and 1955, he made six appearances on The Roy Rogers Show. He also guest-starred in an episode of the American science fiction anthology series Science Fiction Theatre and The George Burns and Gracie Allen Show. In 1953 and 1954, Switzer co-starred in three william A. Wellman-directed films: Island in the Sky and The High and the Mighty, both starring John Wayne, and Track of the Cat, starring Robert Mitchum. In 1956, he co-starred in The Bowery Boys film Dig That Uranium followed by a bit part as a Hebrew slave in Cecil B. DeMille's The Ten Commandments. Switzer's final film role was in the 1958 drama The Defiant Ones.

In early 1954, Switzer went on a blind date with Diantha (Dian) Collingwood, heiress of grain elevator empire Collingwood Grain. Collingwood had moved with her mother and sister to California in 1953 because her sister wanted to become an Actress. Switzer and Collingwood got along well and married in Las Vegas three months later. In 1956, with his money running out and Diantha pregnant, his mother-in-law offered them a farm near Pretty Prairie, Kansas, west of Wichita. Their son, Justin Lance Collingwood Switzer (now Eldridge), was born that year. They divorced in 1957.

In January 1958 Switzer was getting into his car in front of a bar in Studio City, when a bullet smashed through the window and struck him in the upper right arm. The gunman was never caught. That December he was arrested in Sequoia National Forest for cutting down 15 pine trees; he was sentenced to a year's probation and ordered to pay a $225 fine ($1,900 today).

Switzer had agreed to train a hunting dog for Moses Samuel Stiltz. The dog was lost, having run after a bear, and Switzer offered a $35 reward for its return. A few days later, a man found the dog and brought it to the Studio City bar where Switzer then worked. Switzer paid the man $35 and bought him $15 worth of drinks. Several days later, Switzer and his friend Jack Piott, a 37-year-old unit still Photographer, decided that Moses Stiltz should repay Switzer the reward money for the dog. Shortly before 7:00 that evening, January 21, 1959, Switzer and Piott went to Rita Corrigan's home in Mission Hills, where Stiltz was staying, to collect the $50 ($400 today) they felt Stiltz owed Switzer.

In 1987, former Our Gang co-star George "Spanky" McFarland recalled a meeting with Switzer when they spoke about the farm:

Over 42 years later, on January 25, 2001, a third witness came forward and gave his version. Tom Corrigan, son of Western movie star Ray "Crash" Corrigan and stepson of Moses Stiltz, was a child who was present the night Switzer was killed. "It was more like murder," Corrigan told reporters. He said he heard the knock on the front door, and Switzer said "Western Union for Bud Stiltz." Corrigan's mother, Rita Corrigan, opened the door to find a drunk Switzer, complaining about a perceived month-old debt and demanding repayment. Switzer entered the house followed by Jack Piott and stated he was going to beat up Stiltz. Stiltz confronted Switzer with a .38-caliber revolver in his hand. Corrigan said that Switzer grabbed the revolver and Stiltz and Switzer struggled over it. Piott broke a glass-domed clock over Stiltz's head, causing Stiltz's eye to swell shut. During the struggle, a shot was fired into the ceiling and Corrigan was struck in the leg by a fragment. Corrigan's two younger sisters ran to a neighbor's house to call for help. "Well, we shot Tommy, enough of this," he remembers Switzer saying, just before Switzer and Piott started to leave the house.