Robert ("Robbie") Ian Johnston (born 21 August 1967 in Balclutha) is a former long-distance runner from New Zealand who competed twice at the Summer Olympic Games and once at the Commonwealth Games. At the 1992 Summer Olympics in Barcelona he was ninth in his heat of the 5000m and did not advance to the final. At the 1996 Summer Olympics in Atlanta he was 12th in his heat of the 10000m and did not advance to the final. At the 1994 Commonwealth Games in Vancouver he did not finish the 10000m.
Johnston's best international result was fourth in the 5000m metres at the 1994 World Cup in Athletics representing Oceania.