Come the end of the campaign the 21-year-old will then put pen to paper on a three-year deal, with his Parkhead contract expiring in the summer.
Easter Road boss Shaun Maloney knows Henderson well, having coached him at Celtic, and described him as an “extremely talented player”.
"Ewan has superb awareness and vision, he’s creative and will provide assists,” Maloney said.
“He’s a player I really want to help to develop so he can show the league the talent he has.
“As a club, we look forward to helping Ewan develop so he can achieve his potential over the coming years.”
Henderson follows in the footsteps of elder brother Liam who made 46 appearances for Hibs, scoring six goals and laying on 16 more, including the equaliser and winner in the 2016 Scottish Cup final.
Capped by Scotland at Under-17, Under-19, and Under-21 level, the attacking midfielder has made appearances for Celtic in the Scottish Premiership, Europa League, and Champions League, and has spent time on loan at Dunfermline Athletic and Ross County.
Henderson scored in Celtic’s 3-2 victory over Spanish side Real Betis last month in the Europa League – his 11th senior appearance for the Hoops.
He is the second signing in as many days made by the Capital club after 19-year-old striker Elias Melkersen signed on a four-and-a-half year deal after leaving Norwegian champions Bodø/Glimt.
Henderson will wear the number 80 shirt for Hibs.