(Jack English | Focus Features) Gary Oldman plays Winston Churchill, in the biographical drama "Darkest Hour," directed by Joe Wright.

This image released by Focus Features shows Gary Oldman as Winston Churchill in a scene from "Darkest Hour." (Jack English/Focus Features via AP)

This image released by Focus Features shows Lily James as Elizabeth Layton, left, and Gary Oldman as Winston Churchill in a scene from "Darkest Hour." (Jack English/Focus Features via AP)

This image released by Focus Features shows Kristin Scott Thomas as Clementine, left, and Gary Oldman as Winston Churchill in a scene from "Darkest Hour." (Jack English/Focus Features via AP)

This image released by Focus Features shows Gary Oldman as Winston Churchill, left, and Ben Mendelsohn as King George VI in a scene from "Darkest Hour." (Jack English/Focus Features via AP)

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It’s an odd thing to hear Winston Churchill laugh, but laugh he does — in the face of his political opposition, the weight of history and Adolf Hitler — in “Darkest Hour,” a historical drama that is a showcase for a grand performance by Gary Oldman.

The gaunt Oldman dons a fat suit and plenty of prosthetic makeup, painstakingly designed by makeup artist Kazuhiro Tsuji (“The Curious Case of Benjamin Button”), to portray the gruff, growling Churchill. Oldman finds the humor, the indomitable fighting spirit, in the man lionized as the embodiment of English resilience during World War II.

The script by Anthony McCarten (“The Theory of Everything”) concentrates on a few short weeks in 1940, starting with Churchill’s advancement to prime minister on May 10, 1940. He’s the Tories’ reluctant choice to replace the ineffectual Neville Chamberlain (Ronald Pickup). But soon Churchill finds he’s been handed a poisoned chalice, as it will be difficult to earn his party’s loyalty without support from Chamberlain’s loyalists — chief among them the Viscount Halifax (Stephen Dillane), who becomes Churchill’s foreign minister.

It’s Halifax who insists Churchill listen to French overtures to make peace with the Germans, with Italy’s Benito Mussolini as the go-between. To do so, Churchill believes, would put Britain in the same position Chamberlain left it in: capitulating to Hitler. But tepid backing from King George VI (Ben Mendelsohn), and the Allied forces’ retreat to the beaches at Dunkirk, may leave him little option.

While Churchill is beset by foes on all sides, Oldman has just one adversary: the ridiculously dramatic lighting that director Joe Wright (“Pride & Prejudice”) throws out in every scene. His showy direction becomes a distraction at times, threatening to overwhelm a supporting cast that includes Kristin Scott Thomas as Churchill’s stalwart wife, Clementine, and Lily James as his plucky young secretary.

Once Wright and McCarten get past Churchill’s quirks — his heavy alcoholic intake, his blustering at underlings, his constant cigar smoking — Oldman takes the reins of “Darkest Hour.” It’s his performance, capturing the British bulldog’s oratorical fire but most important his life-affirming lightness, that makes this movie worth sitting in the dark for two hours.