Alexander Johnston may refer to:

• Alexander Johnston (1775–1849), British colonial official and orientalist in Ceylon
• Alexander Johnston (Scottish politician) (1790–1844)
• Alexander Keith Johnston (1804–1871), Scottish geographer
• Alexander Robert Johnston (1812–1888), British colonial official
• Alexander Johnston (artist) (1816–1891), Scottish painter
• Alexander Keith Johnston (1844–1879), Scottish geographer
• Alexander Johnston (footballer) (1881–1917), Scottish footballer
• Alexander Johnston (historian) (died 1889), American historian
• Alexander Johnston (Canadian politician) (1867–1951), Canadian journalist, civil servant and politician
• Alexander Johnston (British Army officer) (1884–1952), Hampshire cricketer and army officer
• Alexander Johnston (businessman) (1774–1864), Scottish mill owner
• Alexander W. Johnston (died 1932), Member of the Legislative Council of Samoa
• Alex Johnston (Australian rules footballer) (1881–1965), Australian rules footballer
• Alex Johnston (rugby league) (born 1995), Australian professional rugby league footballer

• Alexander Johnson (disambiguation)
• Alexander Johnstone (disambiguation)