David G. Lewis was born on May 15, 1839, in Ohio to John and Sarah Lewis. His parents were Welsh immigrants, and his father earned a living as a farmer. Lewis grew up and attended school in Licking County, Ohio. By 1860, he was living in Columbus, Ohio, with his brother Samuel, and he was working as a plasterer.
He enlisted in the Union army on August 8, 1862, and he mustered in as a private in Company A of the 128th Ohio Infantry later that day. The regiment performed guard duty around Sandusky, Ohio, and Lewis mustered out on June 9, 1865.
Lewis settled in Orange, Ohio, after the war. He married Hannah Williams, and they had at least four children: William, born around 1867; George, born around 1876; Grace, born around 1880; and Margaret, born around 1883. He worked as a farmer, and by 1870, he owned $3,000 of real estate and $600 of personal property. He applied for a federal pension in December 1890 and eventually secured one. He died of myocarditis in Orange on June 28, 1910.