Sir Frederick Johnstone, 7th Baronet (1810–1841) was a Member of Parliament (MP) for Weymouth and Melcombe Regis from 1832 to 1835. He was part of the Johnstone baronets family.
The only son of Sir John Johnstone, 6th Baronet, he married in 1840 Lady Louisa Elizabeth Frederica Craven, only daughter of William Craven, 1st Earl of Craven. He died, after a fall from his horse, on 7 May 1841.
Johnstone inherited from his father the Westerhall estate on Grenada, and was paid compensation for it under the Slave Compensation Act 1837.