At age four, Morrone adopted his first pet, a parakeet named Jinxie. By age 18, Morrone’s pet collection had outgrown his parents' house. In 1978, Morrone opened a pet store Parrots of the World. with his business partner Nick Guerra in Rockville Centre, New York. The store has since grown into a large business and as of July 2017 it is still in operation.
Morrone’s television career began as a guest on the News 12 program The Family Pet. In 1995, he started a cable show, Extra Help Pet Show, later renamed Metro Pets. His practice of crowding dozens of animals in a small space on-camera was allegedly born of necessity — Morrone claimed it was needed to keep the animals warm in the unheated television studio. Because there were so many animals of different species all together, this resulted in frequent fights between the pets, including a Monkey attempting to eat a Bird's head and a Turtle trying to bite a Dog's tongue off. Morrone - with childish laughter and light-hearted jokes - would downplay these relatively violent incidents. The local cable show led to Morrone’s guest appearances with Martha Stewart on her television program Martha Stewart Living, starting in 1997. In 2001, Hearst Entertainment began syndication of The Pet Shop With Marc Morrone. Marc Morrone and his store Parrots of the World has helped foster animals of victims of 9/11 and many many animals after Hurricane Sandy. Along with helping during intense times of need, he is always available at any time to help people's pets.
In 2003, Martha Stewart Living Omnimedia gave him a half-hour show, Petkeeping with Marc Morrone. The program is taped on location in his pet store.  Morrone was also a frequent contributor to Kids magazine, also published by Martha Stewart Living Omnimedia, and currently hosts a weekly radio program Petkeeping for Martha Stewart Living Radio, on Sirius Satellite Radio.
In March 2006 Morrone was featured on Mag Rack, in the Video On Demand series The Pet Shop with Marc Morrone. The program follows a similar format as Petkeeping, and aims to offer helpful and useful advice on caring for a variety of animals. It also includes appearance by his pets including Harry, a scarlet macaw; Splash, a ferret; and Harvey, a 13-pound Flemish rabbit. 25 episodes were developed for the first season, and cover various topics such as alternatives to dogs as pets, housetraining pets, caring for smaller animals, and tips on setting up and maintaining aquariums.
On August 15, 2007, robbers broke into Morrone's Parrots of the World store through a back window and stole 45 parrots, including cockatoos, African greys, and a toucan. The lot was valued at over $60,000. Morrone expressed concern for the pilfered parrots because they require special food and care and could die if they become overstressed. None of the stolen birds were Morrone's pets that have appeared on television with him, although many of them also live in the store.
Morrone has authored five books, Ask The Dog Keeper, Ask The Cat Keeper, Ask The Fish Keeper and Ask the Bird Keeper, all published by Bowtie Press in 2009. A Man For All Species, a book about the adventures of an animal keeper, was published by Random House in 2010.