Launch from Cape Canaveral; landing 650 km southwest of Bermuda-Islands in the Atlantic Ocean.

It was the first launch, which was broadcasted on television to twelve European nations using the satellite "Early Bird" and for the first time Mission Control Center in Houston, Texas, was used.

First EVA of an U.S. astronaut (White in 23 m). He used a hand-held maneuvering gun; with bursts from this zip-gun he was able to "walk" around the capsule, but after short time the compressed oxygen fuel bottle was empty. He was also able to mount and dismount the camera and move and removed electrical connections from outside the capsule, but had big problems to come back into the capsule, because there were problems to lock the hatch. McDivitt had to help him. After the door was latched White sat back, physically exhausted, sweat streaming into his eyes and fogging his faceplate. McDivitt also felt tired, so they rested before extending a radio antenna to find a ground-based voice and tell Earth all was well. But the first EVA was successful.

All secondary objectives were met except one. The secondary objective of station keeping and rendezvous was only partially successful because separation and rendezvous was not attempted due to fuel consumption. All in all 11 scientific experiments were performed, including observations, photography work; the engineering experiment Electrostatic charge gave higher readings than expected. Onboard were also a Proton-Electron Spectrometer and a Tri-Axis Magnetometer. One medical experiment was the Phonocardiogram experiment, which had sensors attached to their bodies that measured heartbeat rates, especially during liftoff, EVA, and reentry.

Gemini 4 missed its mark by 80 km, but within a few minutes the capsule was recovered by the USS Wasp.