In 2013, Kalezić became more prominent by competing in series 1 of X Factor Adria, the Serbian pan-regional version of The X Factor. During the Podgorica, Montenegro auditions, he sang Beyoncé's "End of Time", successfully advancing to the bootcamp for the "Over 27" category, mentored by Željko Joksimović. He sang "Get Lucky" and "Cosmic Girl", and was then promoted to the Judges' house stage, where he performed "Ljuljaj me nezno", being mentored by Joksimović, who was assisted by Tony Cetinski, but he failed to make it to the live shows and the Final 14.
After ''X Factor Adria''
In 2014, subsequent to X Factor Adria, Kalezić released the albumSan o vječnosti. Singles included most notably "Krivac", "Feel the Music" and "Freedom".
Eurovision 2017
Kalezić was confirmed to be internally selected as the Montenegrin entrant to the Eurovision Song Contest 2017 with his song, "Space", on 29 December 2016. He represented Montenegro in the Eurovision Song Contest 2017 with the song "Space". It was written by Adis Eminić, Iva Boršić, Momčilo Zeković and produced by Stefan Orn and Jovan Radomir in studios in Stockholm.. Montenegro was drawn to compete in the first semi-final of the Eurovision Song Contest which took place on 9 May 2017. Performing during the show in position 6, "Space" was placed 16th in the first semi-final and therefore was not in the top 10 entries of the first semi-final, so did not qualify to compete in the final.
In UK ''The X Factor''
In July 2017, he auditioned for the fourteenth series of the UKThe X Factor. During his audition he revealed that judge Louis Walsh, who was also at the Contest in Kyiv as a member of the Irish delegation, advised him to audition. He received a "Yes" from three of the four judges and progressed to Bootcamp. He survived Bootcamp and progressed to Nicole Scherzinger's Judges' House. At Judges' Houses he was not selected by his mentor Nicole Scherzinger to go through to live shows and therefore was eliminated from the competition. He was included as a potential wildcard act but did not get enough votes from the public.
Eurovision 2018
Kalezić was invited by RTP and OGAE Portugal to travel to Lisbon and perform at a number of events during the 2018 Eurovision Song Contest. Slavko performed remixes of his Eurovision 2017 song "Space" along with new single "El Ritmo" at the Eurofan Café, Wiwijam, Trumps Lisboa and Euroclub.He also attended the semi final in which Montenegro were competing as well as the Grand Final.
''Moja Istina''
In April 2018 Kalezić published a book called Moja Istina documenting his experience at Eurovision 2017 and The X Factor. It was published in Montenegrin language with a view to having it translated to English later on.
