He signed his first professional contract in August 2014 with another Ukrainian club, Dnipropetrovsk's "Dnipro".
He made his debut in the Ukrainian Premier League on April 30, 2017 in a match against Lutsk "Volyn".
He moved to "Kolos" in the 2018/19 season, having played 15 matches in which he scored 3 goals. Together with "Kolos", he made his way to the UPL this season, where he made his debut quite successfully, scoring 3 goals in the first eight matches of the season. However, on November 3, 2019, in the game against "Olympic", he suffered a serious knee injury and for the second time in his career was forced to lie on the operating table and miss a very long time. Denis returned to the game that season more than six months later, on May 30, 2020, coming on as a substitute in a match against Chernihiv's "Desna" and playing 7 minutes.
Denis Kostyshyn is the most popular "Kolos" player among instagram users, having almost 29,000 subscribers on his page as of the end of March 2021.