Jim Parsons works magic in the Roundabout Theatre Company’s revival of Harvey. I had my doubts that this old chestnut would have much impact these days. But Mary Chase’s 1944 comedy, which won the Pulitzer Prize and enjoyed 1,775 Broadway performances in its original run, sparkles anew thanks to this talented actor’s ineffable charms.

He certainly had tough competition from Jimmy Stewart, whose performance is immortalized in the classic 1950 film version. But the Emmy-winning star of The Big Bang Theory manages to make the part his own and then some--no small feat.

The play, which hasn’t been seen on the Great White Way since a 1970 production starring Stewart and Helen Hayes, concerns Elwood P. Down, an exceedingly courtly, mild-mannered man who happens to have a particular eccentricity. His constant companion is the title character, a 6’3” white rabbit who no one else seems able to see.

The situation naturally concerns his family, including his sister Vera (Jessica Hecht) and niece Myrtle (Tracee Chimo). But when Vera attempts to have her brother committed to a sanitarium, she’s the one who’s mistakenly committed instead of him.

Naturally, this leads to all sorts of complications, especially since Elwood charms the bejeesus out of everyone with whom he comes into contact. And, judging by the doors opened and pages turned by the invisible creature who Elwood describes as a “pooka,” he may not be so imaginary after all.

But when things are eventually straightened out and Elwood is about to receive an injection that will forever rob him of his delusions, Vera is forced to decide whether that’s such a good thing after all.

The play’s theme of carefree insanity versus reality’s hard truths has since been echoed in any number of works, including A Thousand Clowns and One Flew Over the Cuckoo’s Nest. But it still has a resonant poignancy that is beautifully captured in director Scott Ellis’ moving and funny production.

That it succeeds to the extent that it does is largely due to its star, who delivers a portrayal that is only comparable to his Big Bang character in its off-the-wall quirkiness. But unlike the obliviously obnoxious Sheldon, his Harvey is so charming that he immediately wins the audience over. There was no doubt about Parsons’ chops and perfect comedic timing, but his ability to so effortlessly shift gears here, not to mention seem perfectly credible for the period, is a revelation.

He’s well supported by the excellent supporting cast, which also includes such veterans as Charles Kimbrough as an increasingly flustered psychiatrist and Carol Kane as his wife. Rich Sommer also scores big laughs with his blustery turn as a sanitarium attendant resistant to Elwood’s charms.

But it’s Parsons who carries the revival on his shoulders, and he succeeds magnificently. But evening’s end, you’re likely to find yourself seeing an invisible white rabbit as well.

Studio 54, 254 W. 54th St. 212-719-1300. www.roundabouttheatre.org. Through Aug. 5.