The Washington Capitals wanted more depth on defense as they prepared for the Stanley Cup Playoffs in 2018. That's why the Capitals acquired Kempny in a trade with the Chicago Blackhawks on Feb. 19, 2018, two days after getting an up-close look at the 27-year-old native of the Czech Republic in a 7-1 loss.
Kempny signed with the Blackhawks on May 23, 2016, after a breakout season in the Kontinental Hockey League and his first appearance for the Czech Republic at the 2016 IIHF World Championship. He played 50 games for the Blackhawks in his first NHL season, finishing with eight points (two goals, six assists). That was enough to convince Chicago to keep the pending restricted free agent, signing him to a one-year contract on May 27, 2017.