The 31-year-old forward transferred across London on deadline day, with Pierre-Emerick Aubameyang arriving at Arsenal from Borussia Dortmund and Michy Batshuayi moving to the German club on loan.
Henry spent eight years at Arsenal before leaving for Barcelona in 2007 and believes that now seemed the right time for Giroud to call time on his stay at the Emirates Stadium.
“We all knew it was going to be a matter of when," Henry told Sky Sports .
“That domino effect that started with Aubameyang coming to Arsenal. That allows Giroud to go and that allows Batshuayi to go.
“It is a weird one because you could feel yesterday, when he went to clap the Arsenal fans, you could sense there was something a bit more into it.
“He did what he had to do for Arsenal."
Having lifted the Premier League trophy last season, the Blues are once again ahead of the Gunners in the standings with eight points and three places separating the sides. With Giroud only featuring sporadically for Arsene Wenger, Henry finds no fault in his compatriot's decision to go to Chelsea.
“On the other side, the World Cup is coming, Chelsea are coming for you, they’re ahead of Arsenal at the minute, Arsene is not playing you," he continued.
“A lot of players are in front of you. I cannot fault him or be upset with him.
“He adds another option up front where he likes to play. Very much the way Antonio Conte wants to play, a target man with a brain.
“I wish him all the very best. But we lost, at Arsenal, a member of the supporting cast.”