Shields was born at his family's estate "Clinchdale", near the early pioneer settlement of Bean's Station, Tennessee in Grainger County. His education as a youth was by private tutors, a sign of the family's affluence. He studied law and was admitted to the Tennessee bar in 1879. He practiced in the counties surrounding his home until 1893, when he was named Chancellor of the former 12th Chancery Division. The next year, he resumed private practice in nearby Morristown, in Hamblen County.

In 1902 Shields became an Associate Justice of the Tennessee Supreme Court, an office which he held until 1910 when he was named Chief Justice. He resigned that post in 1913, becoming the last Tennessean elected to the U.S. Senate by the Tennessee General Assembly prior to the 17th Amendment coming into effect. Shields was popularly reelected in 1918 but in 1924 lost the Democratic nomination to Lawrence D. Tyson, and returned to the private practice of law, this time in Knoxville.

While in the Senate, Shields served as the chairman of several committees. He chaired the Committee on Canadian Relations in the 63rd and 64th Congresses, the Committee on Interoceanic Canals in the 65th Congress, and the Committee on the Sale of Meat Products in the 66th Congress.

Shields died at his estate "Clinchdale" and is buried in Knoxville's Memorial Cemetery.