John Pascoe Grenfell (20 September 1800 – 20 March 1869) was a British officer of the Empire of Brazil. He spent most of his service in South America campaigns, initially under the leadership of Lord Cochrane and then . He was the nephew of British politician Pascoe Grenfell and grandfather to General Sir John Grenfell Maxwell. In Brazil, he rose to the rank of admiral and for his achievements was made a knight grand cross of the Imperial Order of the Rose and a knight of the Imperial Order of the Southern Cross.