He was raised in Prince Edward County, which he represented for many terms in the Virginia House of Delegates; he also served as that body's speaker between 1805 and 1807.

Johnson, a merchant, emigrated to Virginia and initially conducted business at Osborne's on the James River before moving to Prince Edward County.

He resigned that position in 1782, and joined the light corps formed by General Greene, as an adjutant with the rank of Captain.

[3] In 1811, legislators elected Johnston as judge on the general and superior court for the 13th district, which included Prince Edward County.

The reason for the exchange is said to have been that Prince Edward was becoming so thickly settled that Judge Johnston thought hunting would be better in the far southwest.