The Senators planned a news conference for 11 a.m. ET on Tuesday, at which it was expected the hiring would be announced.
The Senators fired coach Cory Clouston and two assistants in April after the team failed to qualify for the playoffs for the second time in three seasons.
MacLean has spent the past five years as an assistant in Detroit, helping the team win the Stanley Cup in 2008. He and Red Wings coach Mike Babcock also worked together for two years in Anaheim, taking the Ducks to the Stanley Cup finals.
MacLean spent 11 seasons in the NHL, playing in 719 games for Winnipeg, Detroit and St. Louis from 1980-91. He finished with 324 goals and 349 assists.
Prior to the joining the Anaheim coaching staff in 2002, the Antigonish, Nova Scotia, native was head coach of the Quad City Mallards of the United Hockey League. He also spent time coaching minor league teams in Kansas City and Peoria, Ill., and has been both an assistant coach with the Phoenix Coyotes and a scout for the St. Louis Blues.
In Ottawa, MacLean will be working for general manager Bryan Murray, his old boss in Anaheim. Murray, who recently received a three-year contract extension, has fired three coaches since he left the job himself to become GM after helping the Senators reach the Stanley Cup finals in 2007.
Ottawa made the playoffs in 2009-10, but finished last season near the bottom of the Eastern Conference with a 32-40-10 record.
ESPN.com hockey writer Pierre LeBrun and The Associated Press contributed to this report.