United confirmed Sporting boss Amorim, 39, has signed a contract until June 2027 with the Premier League club and will officially start in the role on November 11.
The Portuguese was United's top target and the only candidate they spoke to after sacking ten Hag on Monday.
In a video post on X, former England centre-half Ferdinand said: "I spoke to (former Manchester United and Sporting winger) Nani the other day and he said whatever you want to talk about, tactics or whatever, the players play for him, they love him and they respect him.
"One of the issues I think with Erik ten Hag.......and what Nani said about Amorim, is that he's very straight and very direct.
"I'm talking to people who played for him, I think the character and the charisma compared to ten Hag will be the big difference."
Current United defender Diogo Dalot described Amorim as "a fantastic coach" and said Portuguese coaches had a habit of being successful in the Premier League.
Dalot told Sky Sports: "He is a fantastic coach and knows what he wants. Very demanding is what I can expect. It's a perfect match for a club like this.
"The Premier League suits people from Portugal. We have a culture of constantly trying to improve ourselves as we come from a small country.
"I really hope that it is one more case. I am really excited to start working with him."
Manchester City manager Pep Guardiola welcomed the entrance of his new cross-town rival with the declaration: "Welcome to United, to England. I congratulate him."
Guardiola will actually come up against Amorim next week when he takes his City side to Lisbon to face Sporting in the Champions League.
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