The Stoke City centre-back suffered a devastating cruciate ligament rupture just over a year ago and missed most of the 2021-22 season during his recovery.
Souttar also remained absent over the summer and autumn months before the World Cup, but he was given the green light to play the full 90 minutes against Luton Town on November 8.
The 24-year-old earned a place in the Socceroos' World Cup squad for the 2022 edition after his successful rehabilitation, and he has been training as normal in Qatar so far.
Doubts persisted over whether Souttar would start the game, but Arnold has affirmed that the Stoke man is ready to feature from the first whistle against the current holders.
"Harry Souttar is in great shape, he has done all the sessions and brings great leadership and energy to the group and is fit, ready to start the game," Arnold told a press conference.
"Just before he got injured, there was talk that he would go to Everton or a Premier League club for a huge amount of money and unfortunately that didn't happen.
"But Harry has the mindset that these things happen for a reason in life. And then he also has the mindset to bounce back and be ready for whatever comes his way.
"Again, I've known these players for four and a half years and I know their way of thinking, so I know what they are mentally strong and which ones really have only one vision, and that is to move on in life and Harry is definitely one of them."
The Socceroos prepare to begin Group D having lost Hibernian attacker Martin Boyle to a knee injury, with Marco Tilio being called up to replace the 29-year-old.
Despite Boyle's bad luck with injuries, Arnold has affirmed that the striker remains in "great spirits" and is confident that Tilio can perform on the biggest stage for Australia.
"The Martin Boyle thing happened, but that's over now and he's in great spirits even though he's been devastated by injury. But it also gives a great opportunity to someone like Marco Tilio," Arnold explained.
Hellas Verona playmaker Ajdin Hrustic has also been dealing with an ankle injury for the best part of a month, having sustained the problem against AC Milan on October 16.
Hrustic did not feature in any of Hellas Verona's subsequent five Serie A games before the break - making the bench against Spezia on November 13 - and Arnold has conceded that the midfielder is not ready to start.
"Ajdin Hrustic fully trained with us yesterday. He is in good shape but will start on the bench," Arnold added.
Australia will also take on Denmark and Tunisia in Group D of the World Cup as they aim to avoid being knocked out in the group stage for the fourth time in a row.