After high school, Heinlein applied to Annapolis—submitting one hundred letters of recommendation to his state senator—and graduated in 1929, twentieth in his class, with the rank of ensign. He was married shortly after graduation, though little is known of that union, which ended after approximately one year. In 1932 he married Leslyn MacDonald, an intelligent and politically radical woman who inspired many of his female characters.

Later that year, while serving aboard the destroyer Roper, Heinlein contracted pulmonary tuberculosis and was hospitalized. By 1934, his continual bouts with the disease rendered him disabled and forced his retirement from the military. He went on to study mathematics and physics at the graduate school of the University of California, though recurring illness forced his early withdrawal, and he campaigned unsuccessfully for a district assembly seat in Hollywood.

In 1939, after a failed naval career and a humbling defeat in his political endeavors, Heinlein turned to writing as a way to earn a living. This third career choice proved lucrative. By the early 1940s, he had paid off a large mortgage and was by all accounts a successful writer, having won the respect and admiration of the science fiction community. His first novel, Rocket Ship Galileo, was published by Scribner in 1947, and over the next twelve years, he wrote one book a year for Scribner, creating a highly respected and award-winning series of juveniles. During that time, Heinlein also wrote and published short stories, adult novels, and the script for Destination Moon, widely considered to be the first science fiction film. The movie was nominated for three Academy Awards and won in the category of Special Effects. During this time he was also divorced from Leslyn and married Virginia "Ginny" Gerstenfeld, a friend and colleague from his Navy days.

The Heinleins spent their marriage traveling, writing, entertaining, and working on behalf of many charitable causes—particularly blood drives, a tradition which is carried on by the Heinlein Society. In 1956 Heinlein won his first Hugo Award, for Double Star, and went on to win an unprecedented four Hugos, three Retro Hugos, and in 1975 received the first Grand Master Nebula Award for lifetime achievement from the Science Fiction Writers of America. He earned wide acclaim for novels such as Stranger in a Strange Land, Starship Troopers, The Moon Is a Harsh Mistress, and The Puppet Masters. Robert Heinlein continued writing, participating in political debate, and championing the cause of space travel well into the 1980's, when he retired to Carmel, California, with Ginny. His last novel, To Sail Beyond the Sunset, was published in 1987, one year before his death.