Robert Lee Stewart was born on August 13, 1942 in Washington, DC. He graduated from Hattiesburg High School, Hattiesburg, Mississippi, in 1960 and received a bachelor of science degree in Mathematics from the University of Southern Mississippi in 1964,

Robert 'Bob' Stewart entered on active duty with the United States Army in May 1964 and was assigned as an air defense artillery director at the 32nd NORAD Region Headquarters (SAGE), Gunter Air Force Base, Alabama. In July 1966, after completing rotary wing training at Ft. Wolters, Texas, and Ft. Rucker, Alabama, he was designated an Army aviator.

Captain Stewart was assigned as a fire team leader in the armed helicopter platoon of "A" Company, 101st Aviation Battalion (redesignated 336th Assault Helicopter Company) in Vietnam. He flew 1,035 hours combat time from August 1966 to 1967. On 22 December 1966, Captain Stewart was the aircraft commander of an armed helicopter during the defense of a friendly outpost at Vi Thanh in the Republic of South Vietnam. Responding quickly to the radio call for help, Captain Stewart arrived over the outpost and immediately began flying firing passes at treetop level over the Viet Song battalion to slow its advance on the friendly perimeter. Ignoring the tremendous outburst of fire he drew on each pass, he dauntlessly attacked an enemy machine gun nest. Although his aircraft was hit on one of these passes and lost its hydraulic power, Captain Stewart calmly expended his ammunition on the insurgents and flew back to his staging area. After his helicopter was repaired and rearmed, he returned to the battle just as strike planes began hitting the Viet Song with devastating rocket attacks. Captain Stewart flew dangerously close to their strike zone in order to drive away insurgents attempting to creep into the perimeter of the outpost under cover of a heavy mortar barrage. His helicopter was again disabled by hostile fire, but he retained control of the aircraft and flew to friendly territory. His fearless and aggressive attacks were highly instrumental in enabling the friendly forces to completely rout the Viet Gong battalion , saving the outpost and its 230 refugees. For his bravery under fire on this date, Captain Robert Stewart was awarded the Distinguished Flying Cross, the nation's highest award for valor during aerial combat.

COL Bob Stewart became a NASA Astronaut in August 1979. His technical duties in the astronaut office have included testing and evaluation of the entry flight control systems for STS-1 (the first Space Shuttle orbital mission), ascent abort procedures development, and classified payload coordination. He also served as support crewman for STS-4, and Ascent/Orbit CAPCOM for STS-5. He served as a mission specialist on STS-41B in 1984. STS-41B Challenger (February 3-11, 1984) was launched from Kennedy Space Center, Florida, and returned to land there 8-days later. During the mission, COL Stewart participated in two extravehicular activities (EVA's) to conduct first flight evaluations of the Manned Maneuvering Units (MMU's). These EVA's represented man's first untethered operations from a spacecraft in flight. STS-51J in 1985, his second space flight, was launched from Kennedy Space Center, Florida, and after 98 hours of orbital operations returned to land at Edwards Air Force Base, California. It was the second Space Shuttle Department of Defense mission, and the maiden voyage of Atlantis, the final Orbiter in the Shuttle fleet. During the mission he was responsible for a number of on-orbit activities. COL Stewart has logged a total of 289 hours in space, including approximately 12 hours of EVA operations.