He was graduated from Centre College in Danville, Kentucky, with an associate degree and earned his Bachelor's in Divinity and later honorary doctorate from the Episcopal Virginia Theological Seminary.

During this time in the late 1920s and early 1930s, Bishop Barnwell ran St. Margaret's School, a secondary girls' academy in Boise, Idaho.

September 6, 1932, Boise Junior College opened its doors to about 75 students and fourteen faculty members (eight of whom were full-time).

[2] He told its first graduates,All achievement begins in vision and continues through labor and through faith which is the most misunderstood word in the English language.

On August 30, 1934, a special convention was held at Grace Church, Waycross and failed in twelve ballots to elect a new bishop.

A second session met January 15, 1935 at St. Paul's, Augusta and took nine more ballots to elect Barnwell as the fifth Bishop of the Diocese of Georgia.

During his tenure as bishop, which lasted until 1954 the Diocese grew to 8,156 total communicants with two more churches becoming parishes and four additional missions created.

He went on to speak of "relentless weekends" visiting the scattered churches of the Diocese and "in between he tries to make friends with his wife and others who live in his home town.