TORONTO — Chiwetel Ejiofor arrived, he thought, prepared for the first day of shooting “12 Years a Slave.” To play Solomon Northup, a free man from upstate New York who was kidnapped and sold into slavery and who later chronicled his experience in a book, Ejiofor had studied Northup’s memoir, visited plantations and learned how to, as Northup did, play the violin.

But all that work could scarcely ready him for the intense reality of performing a slave’s labor in a Louisiana summer.

“Then you’re there on the first day and it’s 108 degrees and you’re picking cotton,” he said. “How is that accomplishable? I don’t know how to do this without delirium setting in. Then you realize: Now we’re in it. This is what this is. It is a delirium. It is down the rabbit hole.”

Ejiofor’s titanic and steadfast performance in Steve McQueen’s unblinking portrait of mid-19th-century slavery has already been hailed as the performance of Ejiofor’s career. After Fox Searchlight releases the film Friday, Ejiofor is likely to become a best-actor Oscar nominee and a name pronounced with considerably more familiarity.

Ejiofor initially hesitated at taking on the project, but no longer has any doubts.

“I felt enriched by being in Solomon’s shoes for so long,” he said. “Going to that place was so fascinating and there was such a strength and dignity and duty to Solomon and his soul and his survival instinct that I felt there was as much to take away from it that was redemptive as there was that was harsh or difficult.”