Daigneault will take over a team that has reached the playoffs in each of the past five seasons under Donovan and 10 of the past 11.
The 35-year-old spent five seasons as the head coach of the G League's Oklahoma City Blue, going 143-107 and leading them to the playoffs four times.
Daigneault then became an assistant under Donovan last season after spending four years in that role with him at the University of Florida.
A UConn graduate, Daigneault was a student manager under head coach Jim Calhoun from 2003 to 2007, and he was part of the staff when the Huskies won the national championship in 2004. Upon graduation, he became an assistant coach at Holy Cross in his native Massachusetts.
The Thunder have lost a great deal of talent over the past several years. Former NBA MVP Kevin Durant left in free agency, Paul George was traded to the Los Angeles Clippers and another former NBA MVP in Russell Westbrook was dealt to the Houston Rockets.
After those two trades, expectations weren't high for the Thunder entering the 2019-20 campaign.
Despite that, the Thunder went 44-28 and qualified for the playoffs, although they were eliminated by the Rockets in a first-round series that went seven games.
While it marked the fourth straight year that OKC was knocked out in the first round, there is plenty of reason for optimism in 2020-21 and beyond.
The primary reason is the continued development of young guard Shai Gilgeous-Alexander, who was part of the George trade. The 22-year-old averaged a team-high 19.0 points per game last season and added 5.9 rebounds and 3.3 assists.
OKC also boasts veteran guards Chris Paul and Dennis Schroder as well as center Steven Adams, giving the Thunder a solid core capable of competing at a high level next season and beyond.
Donovan may have run his course as head coach after five seasons, so perhaps a new voice on the sidelines will help the Thunder get over the hump. The 55-year-old parted ways with the team mutually and was named the Chicago Bulls' new head coach in September.
Daigneault was a Donovan understudy and may employ many of the same tactics, but he could also give a fresh perspective as a first-time head coach at the NBA level.