Robert B. Lines was born on July 15, 1848, in Kenosha, Wisconsin, to Henry and Susan Lines. His father was a farmer and harness maker who owned $1,200 of real estate and $4,000 of personal property by 1860. He grew up and attended school in Kenosha, and he worked as a telegraph operator during the Civil War.
He attended Columbian College in Washington, D.C., after the war. He settled in Washington, and he earned a living as a lawyer. He travelled abroad in 1892, and his passport application described him as 6 feet, 1½ inches tall, with brown hair and gray eyes. He died of pneumonia in New Orleans, Louisiana, on April 10, 1895.