Nguyễn Văn Mạnh was a Lieutenant general in the South Vietnamese Army of the Republic of Vietnam (ARVN).
[1]: 114 On 23 November 1966 he was appointed commander of IV Corps, which oversaw the Mekong Delta region, replacing the competent, but corrupt General Đặng Văn Quang.
[1]: 262 During the Tet Offensive Mạnh was preoccuppied with the security of his headquarters at Cần Thơ Base Camp, rather than commanding his subordinate units throughout his Corps Tactical Zone.
[2]: 361 On 23 February 1968 he was replaced as IV Corps commander by Lieutenant general Nguyễn Đức Thắng.
In March 1974 he was made deputy chairman of the JGS for pacification and development in place of Lieutenant general Nguyen Van La who retired because of old age.