Gulley was part of Chicago Fire's youth system from 2009 to 2012. In his three years with Mississippi Fire Juniors, he played in three consecutive SUM/Generation adidas Cups and also trained with the club's first team, PDL and Super-20 sides during the 2010 season. Gulley was also a member of U.S. Soccer's residency program during his time in Mississippi. Gulley also spent time with the Chicago Fire U18 during their 2011-12 campaign where he made 23 appearances and tallied six goals.
Club career
Chicago Fire
On August 11, 2011, it was announced that Gulley signed a homegrown contract with Chicago Fire. Making him the second homegrown signing in club history. He wasn't eligible to make an MLS appearance the club until 2012. He did make a few appearances for the reserve squad in 2011 and 2012 and also made an appearance for the first team on September 14, 2011 in an international friendly match against Mexican powerhouse Chivas de Guadalajara. He has not made an official first team appearance for the club.
Atlanta Silverbacks
On April 1, 2013, Gulley was sent on a season long loan to North American Soccer League club Atlanta Silverbacks after training with them for a month. He made his professional debut for the club on May 21 in a 3-2 victory over Georgia Revolution in the second round of the Lamar Hunt U.S. Open Cup. His league debut came three days later in a 1-0 victory over San Antonio Scorpions.
Return to Chicago Fire
On January 14, 2014 Chicago Fire announced Gulley was re-signed by the club. However, on February 20, 2014 Gulley was waived by Chicago Fire.
Return to Atlanta
On July 7, 2014 the Atlanta Silverbacks officially signed Gulley. He had spent the entire previous season with the Silverbacks on loan from the Chicago Fire. Ironically enough, the Silverbacks next match was a U.S. Open Cup Quarterfinal match against the Fire, in Atlanta.
Return home
On April 15, 2015 the Mississippi Brilla announced the signing of Gulley along with his brother James Gulley. He played has first match for Brilla in an exhibition in a 1-0 win against the Birmingham Hammers on May 16, 2015.
International
Gulley was part of the U.S. Soccer residency program for three years. During his time with the residency program, he capped eight times for the United States U17 national team and scored four goals from 2009 to 2010.
Personal
Referee assault incident
On December 6, 2008, while playing high school soccer for Clinton High School, Gulley's brother was sent off for inappropriate behavior. At the conclusion of the match, Gulley's father, Jim Gulley, came onto the field and assaulted the referee.
2016 drug arrests
In January 2016, Gulley was arrested in Clinton, Mississippi for a shooting incident that occurred at his Clinton, Mississippi home. The January shooting stemmed from a "drug deal gone bad" where Gulley was believed to have opened fire, hitting a subject who was attempting to rob Gulley for illegal drugs, according to the Clinton Police Department. On August 1, 2016, The Clinton Police Department released information that Kellen has been arrested for possession of illegal narcotice with intent to distribute while in possession of a firearm. According to the press release from the police department "Gulley is believed to be a significant dealer of marijuana, powder cocaine, and codeine syrup in Clinton and other portions of the Jackson metro area." On November 3, 2017, Gulley was sentenced to four years in prison for possession of Marijuana with intent to sell. He is currently an inmate in the Mississippi Department of Corrections.
