[2] Born and raised in the San Francisco Bay Area, Hollenbeck began wrestling at the age of ten and took up Muay Thai at fifteen initially to give him an edge against opponents while street fighting.

However, under the guidance of Kru Sam Phimsoutham at the World Team USA gym, he was able to channel his aggression off the streets and into the ring, winning national and North American titles as an amateur nak muay.

[6] In addition to the striking credentials, he also holds a purple belt in Brazilian jiu-jitsu under Ralph Gracie and pursued a career in mixed martial arts between 2007 and 2009, going 5–1 with four submission wins and one KO.

[7] In his first international match-up, Hollenbeck knocked out Shawn Lee inside the opening frame at the Legends of Heroes: Muaythai vs. Kung Fu event held in Pahang, Malaysias's Arena of Stars.

[15][16] Less than a month later, on May 14, 2011, Hollenbeck beat Gregory Choplin by way of unanimous decision to be crowned the WBC Muaythai Interim World Middleweight Champion at Lion Fight: Battle in the Desert 2 in Primm, Nevada.

[23] On August 20, 2011, he made the first defence of his WBC Interim World title with a unanimous decision win over a resilient Simon Chu at Lion Fight: Battle in the Desert 3 in Primm.

[29][30][31] In his sophomore appearance in the MPL, he tasted defeat for the first time in his professional career when he dropped a unanimous decision to Nieky Holzken at Muaythai Premier League: Blood and Steel on November 6, 2011, in The Hague, Netherlands.

[38] He instead kicked off his 2012 campaign against Cyrus Washington at the Legends Muay Thai Championship in his home town of San Francisco, California on April 28 and won with a vicious spinning elbow KO in round one to take the WMC Intercontinental Middleweight (-72.58 kg/160 lb) belt.

[39][40][41] Hollenbeck was recruited by the newly founded Glory kickboxing organization in April 2012[42][43] and was immediately entered into the 2012 70 kg/154 lb Slam tournament, made up of sixteen of the world's best middleweight kickfighters.

[54][55][56] When Jordan Watson was unable to compete against Albert Kraus at Glory 10: Los Angeles - Middleweight World Championship Tournament in Ontario, California, on September 28, 2013, due to visa issues, Ky Hollenbeck stepped in to take his place, completing his comeback from injury.

[61] In an ugly fight where Hollenbeck used his unorthodox style consisting of clinching and spinning back fists, he was able to outpoint the South African for much of the bout and scored a standing eight count with a knee in round two before winning a unanimous decision.