Born in Hawaii, Danny Lockin was raised in Omaha, Nebraska. He began dancing professionally at area fairs at the age of eight. His act co-starred Neal Reynolds, an African American boy with whom he would tap dance, tell jokes, pantomime, and do impressions of famous people. During his junior year in high school, Lockin’s family moved to Anaheim, California, where he graduated from Rancho Alamitos High School. He was cast in leading juvenile roles in regional productions of Gypsy: A Musical Fable, The Music Man, and Time for Everything. After graduation, he immediately began working as a professional actor and dancer. He had an early, and uncredited, role as a young farm boy in the 1962 film version of Gypsy. He appeared in the play Morning Sun in October 1963 with Patricia Neway and Bert Convy, but it closed after nine performances. The New York Times said he “dances with acrobatic suppleness and engaging freshness”. He made his Broadway debut on April 8, 1964, in West Side Story in New York City in the role of Gee-Tar (a role he left on May 3), and appeared as an actor and dancer in a regional production of Take Me Along. Later that year, he was cast in a starring role in the musical Tom Sawyer, which played at the St. Louis Municipal Opera. He replaced Jerry Dodge in the role of Barnaby Tucker in Hello, Dolly! in the winter of 1965, and went across the United States on six traveling productions with several actresses playing Dolly Levi, including Betty Grable, Ginger Rogers, Eve Arden, Dorothy Lamour and Anne Russell. He remained in the role for the movie version of Hello, Dolly!, and when filming for that ended, continued the role in the Broadway version of Hello, Dolly!, where he worked with both Ethel Merman and Phyllis Diller until it closed on Dec. 27, 1970. He had mixed feelings about Carol Channing as Dolly, about whom he once said: “Carol Channing is rather disconcerting. You’ll notice her looking at you with those big baby-stare eyes. Then eventually it dawns on you that the person behind those eyes is, in show business terms, about 200 years old.” He also later expressed unhappiness with the way audiences reacted to Merman in the role of Dolly Levi, and how this changed the show. “She wasn’t Dolly up there, she was Ethel Merman in Dolly clothes. … The audiences came, of course; they came to see the Ethel Merman version. But it wasn’t Hello, Dolly! any more, it was her show. … Channing or Streisand, they were part of a cast, trying to act out a character. But with Ethel Merman—and not just her fault, with the audience, she was such an institution—the rest of us felt like just her chorus boys or her chorus line.”

Lockin had a number of guest-star and incidental roles on television as well. He appeared on Father of the Bride, Dr. Kildare, Mr. Novak, My Three Sons, and the Sid Caesar Show. He did a screen test for the 1965 film version of The Sound of Music, but did not get the part. In 1967, he was cast in a minor role in the film The Graduate, but was contractually bound to continue in a regional production of Hello, Dolly! in Las Vegas, Nevada, and could not take the job. In 1967, Lockin married dancer Kathy Haas, who was a bit-part dancer in a production of Hello, Dolly! in San Francisco. Their son, Jeremy Daniel Lockin, was born in 1969. The couple divorced in late 1969. Lockin was cast in the 1969 film version of Hello, Dolly! on the basis of his dancing. He underwent 13 screen tests before he got the part. He later said that doing the film was “the dream of my life”. He felt a strong need to compete with the film’s director, legendary dancer Gene Kelly. At one point during filming, he did a series of four “butterflies” (a cartwheel in which a person does not put their hands on the ground) while Kelly looked on; Kelly suggested an improvement and, to demonstrate, leaped into six technically superior butterflies of his own. Lockin, chastened, reportedly sulked for three days. In April 1970, he guest-starred on The Dean Martin Show on television.

After his divorce, Lockin went back on tour with Hello Dolly!, continuing his role as Barnaby. He stayed with the tour until it ended; at which point, with his career in decline due to substance abuse issues, Lockin moved into his mother’s apartment in Anaheim. Around 1974, Lockin began assisting his mother in running the Jean Lockin Dance Studio. The studio closed in early 1977, and Lockin began teaching at another dance studio. On the night of August 21, 1977, Lockin (who was bisexual) went to a gay bar in Garden Grove, California. He left the bar with a slight, 34-year-old unemployed medical clerk, Charles Leslie Hopkins (who already had a police record and was on probation at the time). Several hours later, Hopkins called police to say that a man had entered his apartment and tried to rob him. Upon arrival, police found Lockin’s body on the floor of Hopkin’s apartment. He had been stabbed 100 times, and bled to death.[13] His body had also been mutilated after death. Hopkins claimed he had no idea how the dead body got in his apartment. He was arrested immediately. Danny Lockin was interred at Westminster Memorial Park cemetery in Westminster, California.