His father was Joseph Chalmers, who, having moved to Mississippi with his family when James was a boy, settled in Holly Springs in 1839.

Chalmers returned to Holly Springs to read law with an established firm, and was admitted to the bar in 1853.

[2] Chalmers entered the Confederate States Army as a captain and was soon promoted to Colonel of the 9th Mississippi Infantry in 1861.

On February 13, 1862, he was promoted to brigadier-general, and on April 6 was assigned to the command of Second Brigade, Withers' Division, Army of the Mississippi.

[3] When Bragg advanced into Kentucky in the summer of 1862 Chalmers' command was a part of his force, performing its duties with courage and zeal.

In April, 1863, at the request of John C. Pemberton, he was transferred to the Department of Mississippi and East Louisiana and placed in command of the Fifth Military District.

[3] Chalmers bore a conspicuous part in the Battle of Fort Pillow and in all the campaigns of Forrest in north Mississippi, west Tennessee and Kentucky.

[5] His Republican opponent John R. Lynch contested the victory, as he was previously strongly elected from this black-majority district.

[6] Chalmers won re-election and received the certificate of election to the Forty-seventh Congress in 1880, serving from March 4, 1881 – April 29, 1882.

In the fall of 1882, Chalmers ran as an Independent Democrat as part of a fusion ticket supported by Republicans and the Greenback Party, to the Forty-eighth Congress.

[5][7] Chalmers wrote to Republican President Chester A. Arthur in December 1882 about how to defeat the regular Democrats in Mississippi.