As a youth, he attended public school and worked on the family farm in the summer and fall. He attended, for brief sessions, the Beulah Male Institute and the Madison Male Academy.
He was Speaker of the Virginia House of Delegates 1887–1895, and a justice of the state Supreme Court of Appeals 1895–1916. In 1863, he became a private soldier in a North Carolina company of the Confederate Army and served until the end of the war. He then returned to his home but, in 1869, moved to Hanover County, Virginia, and, four years later, to Doswell, Virginia, where he lived for two years.
Because he was devoted to the study of law, he carried on his education by studying at night and, for a while, in the office of Samuel C. Redd.
He was admitted to the bar in 1874 and began practice in Richmond. In 1894 he was elected to the Supreme Court of Appeals.
He was made president of the court on June 12, 1916, but resigned on November 6, 1916. Cardwell died at his home, Prospect Hill, on March 19, 1931, and was interred at Woodlawn Cemetery in Ashland, Virginia.
From 1881 to 1895, he was a member of the Virginia House of Delegates from Hanover County, serving as Speaker from 1887 onward.