During the Vietnam War, Vĩnh Lộc served as the commander of II Corps, which oversaw the Central Highlands from 23 June 1965 until 28 February 1968, replacing Major General Nguyễn Hữu Có.

[1]: 25 In late 1965 COMUSMACV General William Westmoreland regarded the II Corps leadership as shaky.

The local senior adviser, Colonel Theodore C. Metaxis, held similar opinions and, as an alternative, suggested that Vĩnh Lộc be made political governor of the Highlands and his military responsibilities delegated to someone else.

[1]: 135 During the Tet Offensive he was described as spending the early days leading troops in Pleiku like an infantry captain rather than performing his duties as a Corps commander.

[2]: 442 Vĩnh Lộc was eventually replaced by Lieutenant General Lữ Mộng Lan on 23 February 1968.