In a phone call which took place on Tuesday, Mulcair emphasized the importance of getting a response from Egypt's president to a pardon application and a deportation request filed in Fahmy's case.
An Egyptian court sentenced Fahmy to three years in prison on Saturday, marking the climax of a trial in which he had been accused of widely denounced terror-related offences.
The NDP says Mulcair told the Egyptian ambassador Canadians are very worried about the imprisoned journalist.
The party says Ambassador Motaz Zahran acknowledged Mulcair's concerns and agreed to relay them to the Egyptian president.
The NDP says Mulcair also noted that swift action to resolve Fahmy's case by Egypt's president would be noted by the NDP, which would like to maintain the "strong" relationship between Canada and Egypt if the party forms government in the upcoming federal election.
"Mohamed Fahmy is being jailed for doing his job as a journalist. That's why the Canadian government should be doing something to help Mohamed Fahmy," Mulcair said in a statement after the call.
"Prime Minister Harper should pick up the phone and talk to the Egyptian president and try to get some answers as to how this is possible."
The Department of Foreign Affairs has said Canadian government officials have raised Fahmy's case with Egyptian officials "at the highest level" and would continue to do so.
Fahmy was working for satellite news broadcaster Al Jazeera English when he was arrested along with two-coworkers in December 2013 and has always maintained his innocence.
His family has urged the Canadian government to do all it can to set him free.
Also on HuffPost