He received his Bachelor of Science degree in 1948 from McGill University, where his father, Canadian physicist John S. Foster, Sr., was a faculty member.

During World War II, before he received his bachelor's degree, Foster began his career in the Radio Research Laboratory at Harvard University.

He continued in this position until June 1973, serving under Presidents Johnson and Nixon, and under Secretaries of Defense McNamara, Clifford, Laird, and Richardson.

He chaired the "Panel to Assess the Reliability, Safety, and Security of the United States Nuclear Stockpile," created in 1998 by Republican Sen. Jon Kyl of Arizona, a longtime foe of the Comprehensive Test Ban Treaty.

[5] [7][8] Foster was a prominent member of the commission to Assess the Threat to the United States from Electromagnetic Pulse (EMP) Attack, established by the 2001 defense authorization act.

Arnold Trophy (1971), the Crowell Medal (1972), the WEMA Award (1973), and the Knight Commander's Cross (Badge and Star) of the Order of Merit of the Federal Republic of Germany (1974).