He'll be replaced as CEO of the retail landlord on an interim basis by Huw Thomas, who served previously for several years as chief financial officer of Canadian Tire Corp., one of the country's biggest retail companies.
Thomas, who takes on the new role on March 21, is a current trustee and chair of the audit committee at Calloway, which owns and manages about 113 retail centres.
Calloway took pains to note that other members of the current management team will remain and they will focus on executing the existing business plan.
"Calloway REIT has an exciting future," said Thomas. "The trust has a strong balance sheet, a growing portfolio of superior assets and will open some of the most innovative retail and mixed use concepts in Canada in the years ahead."
Mawani said Calloway has an excellent management team in place and the support of partners like SmartCentres and Simon Properties.
"These conditions give me complete comfort leaving the trust at this juncture to deal with priority family matters," Mawani said in a statement.
The trust didn't disclose the nature of the family issues.
The change comes during an important time for Canada's commercial real-estate industry, which is adjusting to the arrival of Target and other U.S. retailers as well as restructuring or growth initiatives by established players.
Calloway estimates its enterprise value at about $6.5 billion, making it one of Canada's most valuable REITs.