In high school, at the Westminster Schools in Atlanta Georgia, Galloway recorded bests of 4:28 in the mile and 9:48 in the two mile; he became the state champion in the latter event.

Running for Wesleyan University, he developed as a competitor, earning All-American honors in cross-country and track, clocking 4:12 in the mile, and noted times of 9:06 in the two mile and 14:10 for three.

In 1970, Galloway became the first winner of the Peachtree Road Race in Atlanta, Georgia.

After three years in the United States Navy, Galloway attended graduate school at Florida State University (FSU), where he earned a master's degree in social studies and met his wife, Barbara, who competed for the FSU women's track team. While at FSU, he became a member of the Florida Track Club team, based at the University of Florida in Gainesville and led by Jack Bacheler and Frank Shorter.

Galloway, along with his Florida Track Club teammates Shorter and Bacheler, made the 1972 U.S. Olympic team, Galloway in the 10K, Bacheler in the marathon, and Shorter in both events. The three spent two months in the mountains near Vail, Colorado, conditioning themselves for the Olympics. According to noted runner and journalist, Joe Henderson, Galloway "should have been an Olympic marathoner", but is sometimes said to have given up his shot at a spot in the longer event to help his friend, Bacheler, to make the 1972 team, although some Olympians, including Steve Prefontaine and Frank Shorter have claimed otherwise.

In 1973, Galloway set an American ten-mile road race record, posting a time of 47:49. He was a member of the U.S. National Track and Field team in Europe, Russia and Africa. In the mid-1970s, he altered his training program to emphasize more rest and less weekly mileage, coupled with a long run every other week — a model that has worked successfully for amateurs and first-time marathon runners since then. The strategy helped extend his competitive career, and at age 35 he ran the Houston-Tenneco Marathon in 2:16:35. Other marks included 27:21 for six miles and 28:29 for the ten kilometer event.

For many years, Galloway has been a key organizer of the Peachtree Road Race, one of the premier 10 kilometer road race events in the United States. Galloway helped the race achieve status as a marquee event by bringing together world-class fields which, in 1977, included Frank Shorter, Bill Rodgers, Don Kardong and Lasse Virén. This brought international recognition to the race, while entries escalated from 1,200 to 12,000 participants by 1980.

In 1978, Galloway co-founded the Avon International Women's Marathon, helping to bring the advent of the women's Olympic marathon. He is also co-director of the Manufacturers Hanover Corporate Challenge.

In 1973, Galloway founded Phidippides, which at one time developed into a nationwide franchise network of 35 running stores. The chain has dwindled, and as of 2006, Galloway owns only two Phidippides stores in the Atlanta area.

In 1975, Galloway ventured into the vacation fitness camp business, and as of 2006, there are three in operation each summer in Colorado, British Columbia, and Squaw Valley, California. Coaches and lecturers have included Runner's World founder, Bob Anderson, Covert Bailey, Joe Henderson, Harry Hlavac, DPM, MEd, Joan Ullyot, MD and the late New Zealand Olympic track coach, Arthur Lydiard. In addition to vacation fitness camps, Galloway Productions conducts fitness seminars and marathon training groups across the United States. His unique training approach has been used by runners and coaches around the globe.

Galloway and his wife live with their sons, Brennan and Westin, in Atlanta, Georgia.