Lieutenant General Jagath Jayasuriya, the incumbent Army chief, is to be appointed the Chief of Defence Staff with effect from August 1.
Major General Daya Ratnayake, the current Army Chief of Staff, will succeed Jayasuriya as the Army Commander.
Jayasuriya has been promoted to the rank of General while his successor Ratnayake has been promoted as Lieutenant General, the ministry said.
Jayasuriya was appointed the Army chief in July 2009 almost immediately after the LTTE (Liberation Tigers of Tamil Eelam) was crushed ending its three decades old fight to create a separate Tamil homeland in the northern and eastern provinces.