Welsh actor Ioan Gruffudd is perhaps best known as Reed Richards from “The Fantastic Four,” AKA Mr. Fantastic, AKA the cast member with the unpronounceable name (it’s YO-an GRIFF-ith). You wouldn’t know it based on his work in that movie, but he’s also a swell actor acclaimed for his performance as Horatio Hornblower in the A&E Television Network miniseries of the same name.

Gruffudd’s bright eyes, oft-furrowed brow and long, boyish face suggest a precocious youngster frustrated because his elders won’t take his brilliant ideas seriously. He’s a perfect fit for the role of William Wilberforce, the 18th-century abolitionist who stood before the British Parliament — a room full of frowning old men in white powdered wigs — and argued for the end of the slave trade.

Wilberforce’s 22-year struggle to pass his antislavery bill is dramatized with surprising vivacity in Michael Apted’s “Amazing Grace,” thanks in no small part to Gruffudd’s strong central performance, as well as supporting performances from a mouthwatering list of British actors, including Rufus Sewell, Michael Gambon, Ciarán Hinds and Albert Finney. Don’t let the powdered wigs fool you — this isn’t some stuffy quills-and-candlelight drama you might catch on PBS.

Steven Knight’s talky, literary-minded script remembers the passion behind the speechifying. Wilberforce, a devoutly religious man who claims to have received Joan of Arc-like inspiration, obsesssively campaigns against the slave trade, even as his physical state crumbles and his friends in Parliament scoot down the benches away from him. The overwhelming opinion in Parliament is in favor of the slave trade, arguing that the British economy depends on it and anyone who disagrees should be treated with suspicion (the British fat cats fear the French Revolution may be contagious). Wilberforce negotiates these dangerous waters with a quick mind, a quick tongue and mounting persuasive arguments, including a sly exploitation of the legal system that strikes a crucial blow at a crucial time.

Gruffudd’s performance is also persuasive. He plays Wilberforce as an almost saintly man — kind, intelligent and a bit whimsical — who looks past the phony rationalizations of his countrymen and sees slavery for the inhumane monstrosity that it is.

Apted directs the movie without pomp and circumstance, simply allowing the conviction of the actors — and the inherent power of the story — to move us without resorting to stylistic bludgeoning. “Amazing Grace” is a gentle history lesson with Gruffudd as our inspiring teacher.