Municipal officials says residents who were evacuated will return home on Sunday.
The city's director general told a news conference the opaque cloud is dissipating, and toxicity levels are below the critical threshold.
The leak began Saturday morning following an industrial accident about 30 kilometres east of Montreal.
About five tons of titanium tetrachloride was released into the atmosphere from the Kronos factory that produces titanium pigment for industrial paint.
Fifteen homes and four factories were evacuated. Officials erected a security perimeter about 400 metres around the factory. Five people suffered health problems from the leak and two were hospitalized.
The leak is believed to have been caused by an equipment break. City and factory officials have said they will conduct a full investigation to find the cause.
The cleanup operation is expected to finish Sunday afternoon, the city said.