Penn continued to work at Vogue throughout his career, photographing covers, portraits, still lifes, fashion, and photographic essays. In the 1950s, Penn founded his own studio in New York and began making advertising photographs. Over the years, Penn's list of clients grew to include General Foods, De Beers, Issey Miyake, and Clinique.
Penn met Swedish fashion model Lisa Fonssagrives at a photo shoot in 1947. In 1950, the two married at Chelsea Register Office, and two years later Lisa gave birth to their son, Tom Penn, who would go on to become a metal designer. Lisa Fonssagrives died in 1992. Penn died aged 92 on October 7, 2009 at his home in Manhattan.