Čolak started his amateur free diving career in 2006 when he entered his first competition, the Submania Cup in Zagreb. Less than one year later, he won his first Croatian championship and broke several national records. Čolak turned professional in 2011 and joined the exclusive group of free diving professionals around the world. 
Čolak was the 2009 Confédération Mondiale des Activités Subaquatiques (CMAS) World Champion and world record holder in a joint event with AIDA International (AIDA), the strongest free diving organization in the world. Čolak dove 244 m in dynamic apnea with fins and won CMAS and overall first place, breaking the CMAS world record.
Čolak was the 2011 CMAS World Champion in dynamic apnea with fins, with a 250 m swim, setting a new CMAS world record, his fourth CMAS world record in his short career. On 16 October 2011, he became the AIDA International world champion in the same event (AIDA World Championship in Lignano, Italy), and set the new AIDA world record of 273 m, surpassing the previous record of 265 m held by Dave Mullins. At the same event he won two gold medals, one silver medal and set a new world record.
Čolak won the 2012 AIDA Team World Championship, held in Nice, France with Veljano Zanki and Božidar Petani as his team mates. This was first appearance and first gold medal for the Croatian team at a team World Championships. In addition to gold medal the Croatian team set the new all time best in points with 840 points, beating the previous record of 839 points set by the Denmark team at Okinawa in 2010.
Čolak competed in 2013 Belgrade Pool World Championship, and won all three gold medals from each of the pool disciplines and set one world record. Goran Čolak won the dynamic apnea without fins finals with a 206 m dive, the dynamic apnea with fins with a 281 m dive, which beat his current world record of 273 m set in 2011. On the third day he won his third gold medal with 8:59 min in the static apnea finals. Čolak was dominating Belgrade World Championship from start to finish, winning every qualification heat and every final heat. His results in qualifications was 182 m in DNF, 250 m in DYN and 8:34 min in STA.
Čolak competed in 2013 CMAS World Games in Kazan, Russia. He advanced Croatian national record in static apnea to 9:18 min and won bronze medal, on the same competition he won two silver medals in dynamic apnea with fins and dynamic apnea without fins with dives of 260 and 194 metres. Čolak was the only male athlete who won medals in all three disciplines in Kazan.
Čolak announced AIDA WR attempt in Belgrade from 21st to 27th of November 2013. He succeeded on the first day with the dive of 225m, adding the 7m to the old record that was held by Dave Mullins from New Zealand. 
Čolak was a member of Croatian national team at AIDA Team World Championship in Sardinia 2014, he was the most successful athlete of entire competition in overall points. He set two Team WCh records, one in static (9:13min), and one in dynamic with fins (250m). Croatian team finished on fourth place after 2 other members, Bozidar Petani and Bruno Segvic earned two disqualifications or red cards in dynamic with fins and constant weight.
Čolak competed in 2014 CMAS European championship in Spain (Tenerife), as a member of Croatian national team. He broke CMAS and overall World Record in dynamic apnea with fins, with a dive of 288m adding 23m to CMAS WR (previously held by Aleksandr Kostyshen from Russia) and 7m to overall WR (adding 7m to his own 281m AIDA dive from 2013). He also won a gold medal in that discipline, with addition to a silver medal he won at the same competition in static apnea 2 days before. 
Čolak is currently AIDA's most successful male athlete from AIDA World Championships with six gold medals and one silver medal.
Čolak broke more than 30 domestic CMAS and AIDA records, won Croatian DYN championship eight times in the row (2007-2014), and he was nominated for Croatian athlete of the year in 2009, 2010, 2011, and 2013, 2014.
Čolak won the Dubai Range Rover challenge for two consecutive years, (2011–2012) and came second in 2013 and 2014.
Čolak announced that on 28 September 2013 he would attempt to break the world record in static apnea on pure oxygen, held by Tom Sietas at 22 minutes 22 seconds. He succeeded, holding his breath on the Zagreb main square for 22:30 min, setting the new Guinness world record. On 20 June 2014 he improved his record to 23:01.
Official world records
|DYN||CMAS||288m||17 Oct 2014||Tenerife|
|STA O2||GUINNESS||23:01 min||20 Jun 2014||Vir|
|DNF||AIDA||225 m||21 Nov 2013||Pančevo|
|STA O2||GUINNESS||22:32 min||29 Sep 2013||Zagreb|
|DYN||AIDA||281 m||28 Jun 2013||Belgrade|
|DYN||AIDA||273 m||16 Oct 2011||Lignano|
|DYN||CMAS||250 m||1 Oct 2011||Tenerife|
|DYN||CMAS||248.52 m||13 Sep 2010||Zagreb|
|DYN||CMAS||244.33 m||22 Aug 2008||Aarhus|
|DYN||CMAS||189.48 m||16 Jun 2007||Split|
World championships medal list
- "Goran Čolak svjetski prvak u ronjenju na dah". Index.hr (in Croatian). 4 September 2011. Retrieved 1 October 2011.
- "Lignano; Dynamic with Fin Results and a New World Record!". aidainternational.org. AIDA International. 16 October 2011. Retrieved 17 October 2011.
- "Svjetski rekord i zlato za Gorana Čolaka u ronjenju na dah" [Free-diving world record and gold for Gordan Čolak]. Vjesnik (in Croatian). 16 October 2011. Archived from the original on 14 June 2012. Retrieved 17 October 2011.
- "Goran Čolak s tri medalje najuspješniji muški natjecatelj na svjetskom prvenstvu u Rusiji" (in Croatian). 10 August 2013. Retrieved 25 August 2013.
- "Goran Čolak oborio rekord! Pod vodom bio 23 minute i jednu sekundu". Večernji list (in Croatian). 20 June 2014. Retrieved 21 June 2014.
- Official website (English) (Croatian)
- Goran Colak, Dynamic No Fins World Record - 225m
- Goran Colak - Freediving World Record 273 m