The eight-episode series follows siblings Ben (Corden) and Lisa (Jones), who have been estranged for several years, with the former moving abroad while the latter settles down in their small English hometown.
An unfortunate event prompts Ben's return to the life he'd worked hard to abandon.
Deadline first reported the casting, with the starry trio joining an ensemble that already includes Tom Davis (The Reluctant Vampire), Rosie Sheehy (Pillion), Susan Brown (Falling), Jason Watkins (McDonald & Dodds) and David Harewood (Pierre).
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Alexandria Riley (Silo), Sylvestra Le Touzel (Intelligence), Gary Lamont (Rivals), Emily Lloyd-Saini (Juice) also star in the hotly anticipated project, among others.
The newly announced guests bring even more star-power to The Choir, with Corden and Jones clearly being highly sought-after collaborators following the staggering success of their Gavin & Stacey reunion specials.
Meanwhile, McAvoy is known for acclaimed turns in The Last King of Scotland and Atonement, as well as fan-favourite sci-fi and fantasy work in X-Men, Split and His Dark Materials.
Lastly, screen legend Broadbent earned a new generation of fans as Professor Horace Slughorn in the original Harry Potter films. The role followed earlier credits in Iris, Moulin Rouge!, Bridget Jones's Diary and Gangs of New York.
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