Born in Hot Springs, Arkansas,[3] Guinn began boxing at age nine and lost in the quarterfinals in the Michigan Junior Olympic Tournament at 139 pounds.

Guinn had an amateur career record of 290-26, twice winning the National Golden Gloves Super Heavyweight Championship in 1997 and 1999 but losing in the Olympic qualification to Calvin Brock.

He knocked out veteran Phil Jackson but then lost his second fight to Sergei Liakhovich, who went on to win the WBO heavyweight title.

[2] In October 2008, Guinn knocked out heavyweight prospect Jean François Bergeron in the second round.

[2] In 2009, Guinn knocked out unbeaten Johnnie White (21-0) in a first-round knockout to move back into contendership status and recently defeated Charles Davis by decision.