The 26-year-old attacker arrives at the Keepmoat Stadium having spent last season at League One rivals Portsmouth and becomes the South Yorkshire side's sixth capture of the summer transfer window.
“I’m really excited to be here,” Hiwula said.
“The way the manager wants to play was a big factor and he’s done really well at other clubs he’s been at so I’m looking forward to working under him.
“Hopefully, I’ll bring some energy and pace in the front line and goals too."
After coming through the ranks at Premier League outfit Manchester City, Hiwula joined Huddersfield Town on a permanent deal in 2015 but spent most of his time at the John Smith’s Stadium out on loan.
Usually deployed as a a winger, he enjoyed temporary spells with Bradford City and Fleetwood Town, before signing for Coventry City in the summer of 2018. In two seasons with the Sky Blues, he scored 14 goals in 49 starts, helping them win promotion to the Championship in 2019/20.
"I’ve been promoted from this league with a previous club so I’m hoping to come in, help the boys out and hopefully we can do it again this season," Hiwula added.
Hiwula follows Ben Close, Kyle Knoyle, Ro-Shaun Williams, Tommy Rowe and Matt Smith through the door at the Keepmoat.