It will be Hagel's third visit to the region as Pentagon chief, and comes as Washington presses ahead with its strategic shift to the Asia-Pacific region despite growing budget pressures and repeated crises in the Middle East.
The first leg of his trip in South Korea will be filled with symbolic moments as he attends celebrations of the 60th anniversary of the alliance between the two countries, a bond that dates back to the armistice that ended the Korean War in 1953.
On Wednesday, Hagel presides over a change of command ceremony for US forces in South Korea, with General James Thurman handing over to General Curtis "Mike" Scaparotti, who will take charge of the 28,500 US troops deployed in the country.
The alliance between Washington and Seoul calls for the American commander to lead South Korea's 640,000-strong force in the case of a war with the North.
President Barack Obama indicated in May that the transfer would go ahead as scheduled, but US officials have not closed the door on the issue, amid concerns over the threat posed by the North's nuclear and missile programs.
"The North Korea provocations cycle is something that Secretary Hagel has handled early in his tenure," said a senior defence official.
The question of when operational control should be passed to the South Koreans will feature prominently in Hagel's talks with his counterpart and President Park Geun-Hye.
