LONDON — Jamael Westman was 14 when he took the stage in his first musical, a school spoof of “Pirates of the Caribbean” called “Pirates of the Curriculum.” After that, he gave musical theater a nice long rest.

But break time is over for Mr. Westman. Now 25 and a year and change out of drama school, he is making his West End debut — and his return to musicals — in the splashiest way possible: playing the title role in “Hamilton,” Lin-Manuel Miranda’s steamroller of a hip-hop hit, in its hotly anticipated British premiere.

“Musicals are not something I’m too familiar with, or have been,” Mr. Westman said one late-November morning at a restaurant in Westminster. Next door, the Victoria Palace Theater was, from the street, a picture of disarray. Major renovations that delayed the start of the show’s run were still underway.

Mr. Westman, by contrast, was utterly composed — thoughtful, quick-witted and funny as he talked about his induction into the world of a juggernaut show whose power and scale didn’t quite hit him until he’d already won the job.