The pop star's costume change came before he performed a rendition of Judy Garland's classic song from the 1939 movie, "Somewhere Over the Rainbow", at Madison Square Garden.
His teenage farm girl outfit was topped off with Dorothy's iconic ruby slippers, rosy cheeks, and a bow.
Harry, who is currently on his "Love On Tour" trek, will perform a second Harryween show at the venue on Sunday night.
Styles is also playing dress up for the movies - he appears as Eros the Titan during the end credits of the new Marvel blockbuster "Eternals".
Guesting on her pal Drew Barrymore's American chat show, she quipped, "This makes me want to dip my toe back into the Marvel Universe."
"Maybe Pepper Potts can intersect with the Harry Styles of it all."
When Drew explained Harry's alter-ego has special powers, including the ability to "stimulate the pleasure centres of anyone within 25 feet," co-host Ross Mathews joked, "This is what they call typecasting."
Drew then wondered, "How does one in the Marvel Universe interpret a god of love and sex? How does that work in the Marvel world?"
And Gwyneth replied, "You just cast Harry Styles. You just put him without a shirt on and there you go."