Robert Johnston may refer to:
- Rob Johnston, assistant general secretary of International Transport Workers Federation
- Robert Johnston (1783–1839), plantation owner in Jamaica
- Bert Johnston (footballer) (1909–1968), Scottish footballer (Sunderland AFC)
- Bob Johnston (1932–2015), American record producer
- Bob Johnston (economist) (1924–2023), Australian economist, governor of the Reserve Bank of Australia
- Bob Johnston (footballer) (1929–2012), Australian footballer for Melbourne
- Bobby Johnston (born 1967), composer and musician
- Robbie Johnston (born 1967), long-distance runner
- Robert Johnston (VC) (1872–1950), Irish rugby union player and soldier
- Robert Johnston (American politician) (1818–1885), American politician of the Confederate States
- Robert Johnston (Canadian politician) (1856–1913), farmer and political figure in Ontario, Canada
- Robert Johnston (cricketer) (1849–1897), Scottish-born New Zealand cricketer who played for Otago
- Robert Johnston (naval officer) (1792–1882), early Australian Navy officer
- Robert Johnston (businessman) (1924–1995), Australian industrialist and businessman
- Robert Johnston (died 1687), English-born politician and judge in Ireland
- Robert B. Johnston (1937–2023), United States Marine Corps lieutenant general
- Robert Daniel Johnston (1837–1919), brigadier general for the Confederate States of America during the American Civil War
- Robert Mackenzie Johnston (1843–1918), Scottish-Australian statistician
- Robert Matteson Johnston (1867–1920), American historian
- Robert Mercer Johnston (1916–1985), Ontario political figure
- Robert Smith Johnston, Lord Kincraig (1918–2004), Scottish judge
- Georgie Fab (Robert George Johnston, born 1952), Canadian rock musician, guitarist, singer songwriter and producer
- Robert S. Johnston, president of Saint Louis University
- Robert Johnston, former guitarist for Life Without Buildings