Luke A. Halpin was born in Astoria, Queens, New York City on 4 April 1947 to Helen and Eugene Halpin. He has one older brother, Eugene, Jr., and one older sister, Joan.
His acting career started when a music teacher, impressed by Luke's "all-American" look, encouraged him to try out acting. Luke turned out to be a natural, and in 1955 he co-starred with Natalie Wood in Studio One's "Miracle at Potter's Farm".
Luke's career blossomed quickly. By the age of 15, he had already appeared on many of the major TV series of the day: Armstrong Circle Theater, United States Steel Hour, Studio One, Kraft Theatre, Harbor Master, Everglades, The Phil Silvers Show, The Defenders, Route 66, Naked City, and Young Doctor Malone.
The bulk of Luke's early career was on the theater stage, and included roles in such projects as Peter Pan, Annie Get Your Gun, Waiting For Godot, and Take Me Along.
Luke got his biggest break when he was picked to star as Sandy Ricks in the 1963 feature Flipper. The film was successful and led to a sequel, Flipper's New Adventure (1964), and the TV series that ran for 88 episodes over three seasons, from 1964 to 1967. Forty years later, the Flipper TV series is still in syndication.
The TV series made Luke very popular among the younger viewers. The athletic actor was normally shown dressed down to little more than cut-off jeans, making him a genuine heartthrob among millions of TV viewers. He was frequently featured in teen magazines like "16", plus Teen Life and the earliest issues of Tiger Beat.
After the TV series, Luke appeared in other feature films, including If It's Tuesday, This Must Be Belgium, Island of the Lost, and Shock Waves. TV guest appearances in the years shortly after Flipper included Judd for the Defense, The Dating Game, Death Valley Days, and Bracken's World. One notable later appearance was in the TV-movie The Ordeal of Dr. Mudd in 1979.