Crosthwaite was educated at Oxford. He entered Indian service in 1857 and was posted to the North-Western Provinces. His first officiating post was as Chief Commissioner of Burma. British India left the Silver Standard monetary system during Crosthwaite’s time in office as Lieutenant Governor of the North-Western Provinces and Chief Commissioner of Oudh. He left and became a member of the Council of India.

Crosthwaite returned to his office as Chief-Commissioner after Bernard's second term. It was midway during this term, on 1 January 1886, that the Kingdom of Awa, 'Upper Burma,' was annexed to British India. He left this post to return to the North-Western Provinces where he was first posted in India. Crosthwaite also briefly covered the post of Chief Commissioner of the Central Provinces. He died in 1915.