In 1962 was selected to play for Ireland. His first Test on 10 February 1962 was against England at Twickenham. Later that year he was selected to tour South Africa with the British and Irish Lions.

McBride continued to play for Ireland throughout the 1960s and played for Ireland when they first defeated South Africa (the Springboks) in 1965, and when Ireland defeated Australia in Sydney — the first time a Home Nations team had defeated a major southern hemisphere team in their own country. He was again selected for the Lions in 1966, this time touring New Zealand and Australia. He toured South Africa with the Lions again in 1968.

He was selected to play for the Lions in their 1971 tour of New Zealand. Despite being criticized by some as being “over the hill”, McBride was made pack leader and helped the Lions to a Test series win over New Zealand; their first and last series win over New Zealand. He received an MBE in 1971 for services to rugby football.

McBride’s leadership qualities led to his appointment as captain of the British and Irish Lions in their 1974 tour to South Africa. The Test series was won 3–0, with one match drawn; the first Lions series ever won in South Africa. It was one of the most controversial and physical Test match series ever played. The management of the Lions concluded that the Springboks dominated their opponents with physical aggression, and so decided to match fire with fire. Willie John McBride instigated a policy of “one in, all in”: that is, when one Lion retaliated, all other Lions were expected to join in the melee or hit the nearest Springbok.

In 1975 as his international career was ending he played his last game for Ireland at Lansdowne Road. The game was against France, and near the end of the match he scored his first test try for Ireland. It was the crowning moment of a great playing career. His last international game was against Wales on Saturday 15 March 1975.

After retiring from playing the game, McBride coached the Irish team and was manager of the 1983 Lions tour to New Zealand. Despite the test results being mainly poor, team camaraderie was high and some good wins were recorded in other games. In 1997 he was an inaugural inductee into the International Rugby Hall of Fame. He lives in Ballyclare. He has been asked to present Test jerseys and give motivational speeches to Lions players prior to matches. In 2004 he was named in Rugby World magazine as “Rugby Personality of the Century”. He is a major supporter of the Wooden Spoon Society.

McBride was awarded a CBE in the 2019 New Year Honours list for services to Rugby Union.