The deal is worth $7 million, according to a source familiar with the situation.
The 23-year-old Frolik came on strong in the playoffs last season with two goals and three assists during the seven-game series against the Vancouver Canucks.
Frolik scored 21 goals in his first two seasons, but he fell off a bit last season with 11 goals, including three with the Blackhawks after being acquired from the Florida Panthers on Feb. 9.
The Blackhawks also agreed to a one-year deal with Sami Lepisto.
Jesse Rogers covers the Blackhawks for ESPNChicago.com.