Born in Wilmington, North Carolina, Purnell graduated from Trinity College (now Duke University) in 1869 and read law to enter the bar that same year.
He was in private practice in Baltimore, Maryland and Salem, North Carolina from 1870 to 1873.
[1] On April 26, 1897, Purnell was nominated by President William McKinley to a seat on the United States District Court for the Eastern District of North Carolina vacated by Judge Augustus Sherrill Seymour.
Purnell was confirmed by the United States Senate on May 5, 1897, and received his commission the same day.
Purnell served in that capacity until his death on December 19, 1908, in Raleigh.