Conrad joined NASA as part of the second group of astronauts, known as the New Nine, on September 17, 1962. Regarded as one of the best pilots in the group, he was among the first of his group to be assigned a Gemini mission as pilot of Gemini 5. Along with his commander, Gordon Cooper, he set a new space endurance record of eight days. He was then named Commander of the Gemini 8 backup crew, and later Commander of Gemini 11 with pilot Richard Gordon.
On November 14, 1969, Apollo 12 was launched with Conrad as Commander, Richard Gordon as Command Module Pilot, and Alan Bean as Lunar Module Pilot. The launch was the most harrowing of the Apollo program, as a series of lightning strikes just after liftoff temporarily knocked out power and guidance in the Command Module.
Conrad's last mission was as Commander of Skylab 2, the first crew to board the Skylab space station.