While at Old Dominion, Purnell enjoyed a highly successful playing career, finishing 18th on ODU's all-time scoring list with 1,090 points and leading the Monarchs to the 1975 NCAA Division II national championship.

During Purnell's tenure as a full-time assistant, he helped ODU reach the postseason seven times (3 NCAAs and 4 NITs).

Purnell is credited with one of the biggest one year turnarounds in NCAA history as his 1990-91 Radford club posted a 22–7 record, a 15-game improvement over the previous season.

After another successful stint, in 1994, he accepted a position as head coach at the University of Dayton where he led the Flyers to two NCAA tournament appearances (2000, 2003) before accepting the head coaching job at Clemson University shortly after the #4 seeded Flyers lost to #13 Tulsa in the first round of the 2003 NCAA tournament.

Purnell was the head coach of the 1999 USA World University Team and led the squad to an 8–0 record and the gold medal in Brisbane, Australia.

[6] At the conclusion of that season, Purnell took his team to the championship game of the NIT, losing to West Virginia in the final, following wins against Syracuse, Air Force, and Ole Miss.

In 2008, he guided the Tigers to a third-place 10–6 record in the Atlantic Coast Conference and a runner-up position in the ACC Tournament in Charlotte, losing to North Carolina by 5 points.

However, Purnell was unable to win an NCAA tournament game (0–6) during his stints with ODU, Dayton and Clemson.