Václav Sivák was born in Ostrava, Czech Republic and grew up with in an excluded Romani locality in Ostrava-Vítkovice.

[5] On 19 April 2018, Sivák faced Fang Feida in collaborative event between XFN and Wu Lin Feng.

[8] Sivák faced Ali El saleh at the Night of Warriors event on 19 December 2020, in his sole fight of the year.

[11] On 18 March 2021, Sivák revealed that he would make his Road to ONE debut against Marian-Florin Soare at Night of Warriors 17 on 24 April 2021.

[12] He won the fight by a first-round knockout, staggering Soare with a knee to the body, before finishing him with a flurry of punches.

[14] He withdrew from the bout the week before, in order to fully heal from the injuries he sustained in his fight with Sugden.

Sivák scored the sole knockdown of the fight in the third round, as he dropped his opponent with a head kick.

[29] He withdrew from the fight on July 28, as a pre-fight examination revealed he had two displaced bones in the hand he previously injured while preparing for the Nabati bout.

[32] Sivák made his first WAKO-PRO World K-1 Light Welterweight (-64.5 kg) championship defense against Anass Ahmidouch at Lucerna Boxing 15 on 30 December 2023.

[34] Sivák faced Michał Królik at XTB KSW Epic: Chalidow vs Adamek on 24 February 2024.

[36] Sivák made his second RFA K-1 -66 kg title defense against Ruslan Toktharov at Adam Król on 16 April 2024.

[39] Sivák faced Konstantin Stoykov at RFA x IAF: Special Title Night 2 on September 28, 2024.