The last time that the north London club won a trophy was during his first stint with the club, when they beat Manchester United in the 2005 FA Cup final on penalties.
Arsene Wenger's men have since endured a barren period that has lasted six years, but the former England international reckons the return of the club's top goalscorer could bring about a change in fortunes.
For now, the Gunners take on Leeds United in the third round of the FA Cup on Monday.
"He has been magnificent against Leeds in the past," Keown is quoted by The Sunday Mirror as saying, in reference to the Frenchman's tally of nine goals in his last five matches against the west Yorkshire club.
"It will be a treat for the fans, the manager and the player himself. It’s like being transported back in time — a fantasy come true for everyone.
"He may be a bit slower. And it might not be till the end of the two-month loan that we see glimpses of what he did before.
"But I think his return will restore Arsenal’s pride. It will energise Arsene Wenger and he’ll be a huge influence on the young stars such as Jack Wilshere and Theo Walcott. Theo idolises him. It could certainly galvanise the team into winning a trophy."
Keown also insists that he had a feeling that Wenger would bring Henry back into the fold after watching him train during the MLS off-season.
"I saw him train with Arsenal on a corporate day and I saw the reaction from Arsene," he said.
"There was a glint in his eye and I wondered if he would bring him back.
"At the beginning of the season, Arsenal had lost a gumshield and were lying on the floor on their backs. Now, they’re on their feet and I think Thierry can deliver a knockout punch. He is the best athlete I’ve ever seen with a pair of boots on."
Concerning the upcoming game against Leeds, Keown added: "It’s one of the big games in English football.
"It’s a shame what’s happened to Leeds since they were in the Champions League semi-final 10 years ago.
"The Premier League has missed them."
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