Sullivan - who has been speaking to Sunday Times - and fellow co-owner David Gold were criticised in some quarters after parting company with Sam Allardyce back in May.
Many pundits felt it was a big risk, citing the fact Allardyce has never been relegated from the Premier League as reason enough to keep him in east London.
After a storming start to last season, the Hammers sat in fourth place by the new year.
But they dropped like a stone in 2015 to finish 12th as Allardyce oversaw just three more wins.
Most Hammers fans had seen enough and wanted change.
They got just that when Sullivan and Gold appointed former Croatia boss and Hammers defender Bilic back in June.
And Sullivan has told the Sunday Times he feels the decision to go in a different direction will be vindicated as Bilic has similarities to Mourinho, the legendary boss of fierce London rivals Chelsea.
"Slaven was probably the fans’ choice and has many admirable qualities," Sullivan told the Sunday Times.
"He’s an incredibly hard-working fellow, he’s really whacking in the hours, and he’s smart, a trained lawyer.
"He’s got stature.
"I think he’s got the fear factor like Mourinho and players will respect that.”
Despite his confidence in the new man in the Upton Park hotseat, Sullivan has also revealed that Bilic's contract at the club will be ripped up if they are relegated.
But he insists that would be the same for any manager they bring in as he feels financially compensating someone who has failed is a 'joke'.
Bilic and Mourinho: How do they compare?
Sullivan's words will not be lost on Bilic as he is a keen admirer of Mourinho as a manager.
“It was really flattering. The guy is class, what can I say,” was Bilic's reaction to being sent a text message by Mourinho after he was appointed West Ham boss, as reported by the Evening Standard at the time.
Mourinho had sought his number from one of his former players Demba Ba, who had been at Besiktas with Bilic.
How do the stats stack up?
It gives a glimpse of the mutual respect between the two but how do they compare statistically?
Well, Bilic currently has a 100% winning record in the Premier League after the most stunning result of the opening weekend, a 2-0 victory away at title hopefuls Arsenal.
Overall in his managerial career, the Croatian has a win percentage of 55.8, with 101 victories in 181 matches. He has drawn 42 and lost 38 along the way, with his worst spell coming after taking over at Lokomotiv Moscow in 2012.
Despite being five years younger, Mourinho is vastly more experienced, with 496 wins from 742 games as a manager.
He has overseen 150 draws and just 96 defeats in seven different spells at various clubs, leaving him with an overall win percentage of 66.85.
While there is a long way to go this season with just one game played, West Ham fans will be happy if Bilic goes on to prove as charismatic, popular and shrewd as Mourinho in what is their last ever season at their Boleyn Ground home of 112 years.