Robert Mackintosh was a native New Yorker born in 1925. He is best known for his costumes for Broadway, but also designed for film, television, and nightclubs. Later in his career, he made a successful foray into fashion design as well.

According to his New York Times obituary, Mackintosh studied at Parsons School of Design before beginning his career as a costume designer. A 1983 article featured in Women's Wear Daily states that Mackintosh graduated from the Pratt Institute. While his early life and the details of his educational background remain unclear, it seems likely that Mackintosh studied art or design at a New York City institution before his career took off in the early 1950s.

Mackintosh was only twenty-one when his work attracted the attention of actress Lena Horne, who hired him to design her stage costumes. At twenty-seven, his costumes debuted on Broadway in the 1952 musical Wish You Were Here. He designed costumes for several other Broadway shows, including Gypsy, The Boy Friend, How Now, Dow Jones, and Silk Stockings. He worked with a number of Hollywood stars, including Marilyn Monroe, Bette Davis, Angela Lansbury, and Barbra Streisand. A career high point came in 1966, when he designed the costumes for the Broadway hit Mame, including twenty-seven costume changes for Angela Lansbury. Lansbury garnered a Tony Award for her performance and Mackintosh won first place in the Variety New York Drama Critics Poll for best costumes. He also designed costumes for the 1983 revival of the production, as well as offstage garments for Lansbury.

Mackintosh was also an active fashion designer in the 1960s and 1970s. In 1965, he began designing the junior petites line, Musette, for teenage girls. Bergdorf Goodman was quick to pick up the collection and place it in their Bigi shop (the sixth floor department for girls thirteen- to eighteen-years-old). In the 1970s he went on to design womenswear for Paul Rogers. Sketches in the collection suggest he also designed menswear during this period.

Mackintosh continued to create costumes in his later years, predominantly for off-Broadway shows. A 1995 feature article reveals that he was hard at work designing costumes for his thirty-first musical, Swingtime Canteen.

Robert Mackintosh died in Manhattan in 1998.