The Norwegian midfielder was brought back to British football in January by Ole Gunnar Solskjaer, as he looked to his homeland for new recruits shortly after inheriting the Bluebirds reins.
Cardiff were able to convince the 19-year-old that Wales was the perfect destination for him, despite United holding an option on his services.
With Daehli having previously spent time in the youth ranks at Old Trafford, the Red Devils had first refusal once it became clear that he would be moving on.
The youngster worked with Solskjaer at former employers Molde, though, and believes another spell under the ex-United striker will be of greater benefit to his ongoing development.
He said: "I went to Manchester United as a 15-year-old and it was my dream to play for them.
"But I know the Cardiff manager so well and wanted to play for him again.
"It felt safe to choose Ole. He knows me and what I stand for as a player. I was sure that he would give me the chance, and he did. So I believe that I did the right choice."
Solskjaer is delighted to have Daehli at his disposal again, with it his opinion that the Norway international has the potential to become one of the Premier League's top creative influences.
He said of a player who has already been likened to David Silva and Samir Nasri: "I don't wish to compare him to others and he doesn't need any extra pressure, but he is the type of player who likes to get between defensive lines, take people on and create openings.
"When you look at the Nasris, Silvas and that type of player, you look at Mats and think he could end up as similar in his style.
"Signing for Manchester United was an option for him, but he chose Cardiff and that shows how much he wants to succeed for this club."
With the backing of his boss, Daehli is now looking to kick on and prove that he can be a key performer in the English top flight.
He added on his time at Cardiff so far: "It's gone okay. It's a level up from the Norwegian League and I have to adapt, but I've loved it.
"To be honest, I did not know what to expect of English football.
"But I'll always have belief in myself and that I can do well for Cardiff City.
"Every time I go onto the pitch my aim is to show that I should start the next game. That is what's important for me."