He enlisted in the Sri Lanka Navy as an Officer Cadet in its 11th Intake on 15 November 1982, undergoing basic training at the Naval and Maritime Academy, Trincomalee, where he was adjudged the best cadet and selected for an international midshipmen course at the Britannia Royal Naval College, Dartmouth, which he attended between 1984 and 1985.

Ranasinghe has held the command of various ships and craft during his career in the navy, including SLNS Samudura (Commissioning Commanding Officer of US Coast Guard Cutter received from the United States of America), and the Fast Attack Squadron between 2002 and 2004.

President Maithripala Sirisena appointed Ranasinghe the Chief of Staff of the Sri Lanka Navy with effect from 11 July 2015.

[2] Ranasinghe was appointed Commander of the Navy effective 26 October 2017, replacing Travis Sinniah.

Ranasinghe was appointed Chairman of Sri Lanka Ports Authority on 3 October 2024 by President Anura Kumara Dissanayake.