MacGregor grew up in the Philadelphia area, and it was there that he did his first performing, as a disc jockey, recording engineer, and singer/guitarist. MacGregor played Scottish, folk, and novelty songs, with an occasional children's song thrown in. After setting up a radio station in Daytona, FL for Army Special Services, MacGregor returned to help with the birth of television in New York City. He was the master of ceremonies and performer on a children's program called Scrapbook.
About this time, MacGregor produced about 200 novelty records, such as A Record from the Easter Bunny. The recordings were produced on cardboard acetate and sold through the Woolworth variety store chain for 25 cents apiece. MacGregor joined ASCAP and composed numerous pop ballads as well, recorded by Rosemary Clooney, the Four Aces, Teddy Wilson, and others.
In the early '70s, MacGregor created three albums. The simple guitar and voice recordings were outshone by the wacky lyrics within. Volume One, called Folk Songs for Kiddies, had a note on the back that said "This record was produced by Martin Braunstein because of a firm belief that it unquestionably could become the most precious album in any collection." With songs like "Sneezy the Polar Bear" and "Big Storm in a Bathtub," the album was nothing like the saccharine productions of the major labels. Volume Two, Tops in Pops for Kiddies, contained such gems as "Three Jolly Apes," about primates who create a nut famine, and "Old Fat Froggie," who bounces apples off the heads of kids. The third volume, Command Performance for Kiddies, contained another dozen original songs, including "There's No Room in the Toy Box Anymore" and "Don't Shoot Those Guns Anymore." MacGregor's strong feelings about commercialism and violence in regard to children were gently stressed through his songs. From his point of view, "Looked at from the perspective of the younger generation, the world around them bears little resemblance to Disneyland."
Although not widely distributed, the three volumes still received airplay nationally on public radio stations. In later years, MacGregor worked to re-release these albums (as well as many of his singles) on cassette, and kept track of a large collection of classic children's albums.