Joseph J. Lhota, the chairman of the authority, said Mr. Byford had been on the radar of transit officials for years — dating back to his participation in a 2014 commission appointed by Gov. Andrew M. Cuomo to examine how the authority could be improved. But despite producing recommendations that are now considered essential, like investing in basic infrastructure, the commission’s findings were largely ignored. Still, when Mr. Cuomo put together a similar panel this summer, Mr. Byford was once again included.

From the outset of the search for a new leader three months ago, Mr. Byford was a top contender. He has been considered a rising star in the transportation world with a deep resume that includes stops in Sydney and London before he went to Toronto, where, Mr. Lhota said, his record of achievement convinced officials that he was up to the task.

“He knows how to change the culture of an organization,” he said. “We were looking for a certain level of transit expertise combined with the political skill and moxie.”

Mr. Cuomo met with Mr. Byford after he had received the backing of the Transportation Authority and was blunt about the challenges he would face, a conversation that Mr. Lhota said reinforced what Mr. Byford already knew.

“He is an astute student of what New York City has done and not done,” Mr. Lhota said.

Mr. Byford, in a brief telephone interview, said he was impressed by the passion both Mr. Lhota and the governor brought to the subway’s plight, but was under no illusions about the situation he is inheriting.