He was appointed to United States Military Academy, graduating with the class of 1934 and was commissioned a second lieutenant in the 16th Field Artillery at Fort Myer, Virginia.

As a major general in 1965, Seaman was named commander of the 1st Infantry Division at Fort Riley, Kansas.

In 1967, Seaman returned stateside and assumed command of First United States Army at Fort Meade, Maryland.

Seaman was the deciding official in cases of 13 officers involved in the failure to investigate or cover up the 1968 My Lai Massacre during the Vietnam War.

Seaman died at the Veterans Administration Hospital in Charleston, South Carolina, on February 18, 1986, at age 74, He was buried at the Beaufort National Cemetery.