Bell has signed a two-year contract at Tannadice after leaving Rangers and was instantly impressed by McKinnon.
"I spoke to a couple of managers in the top flight and a couple of teams down south," said the 29-year-old keeper.
"I spoke to the manager here early on in the month and I had kind of made my mind up."
McKinnon, who was in charge of Raith Rovers last season, took over from Mixu Paatelainen after the Finn was sacked following United's relegation from the Premiership.
"It was just the way he came across and sometimes you need to go with your gut feeling," said Bell.
"He came across so well and so determined. I knew this was the club for me."
Out of favour at Rangers, Bell cut a frustrated figure last season at Ibrox as he spent the season on the treatment table and then on the bench as Wes Foderingham kept him out of the team.
"It was difficult," he said. "Starting off, I was injured for the first five months of the season, so that was hard.
"When I got back fit, obviously the manager brought in a new goalkeeper, so I thought I was going out on loan, but things changed and it didn't happen.
"I ended up sitting on the bench, which I didn't really want to do.
"Wes had a good season, so I couldn't go chapping on the door too much.
"I had a chat with the manager at the end of the season and it was all agreed that I could go and try and find first-team football and, when Dundee United spoke to my agent, things started moving on."
Bell believes United should be in the top six of the Premiership and is determined not only to help the club return there but recapture the form that led to his solitary Scotland cap in 2010.
"We know it is going to be difficult," he added. "The Championship is a really difficult league - I have been there two years now.
"We have got a really strong squad and I am sure the boys will be up to the challenge.
"After the last year I have had at Rangers, I am really determined to get my career back on track and prove I am the goalkeeper I was."
Cammy Bell says new Dundee United manager Ray McKinnon was the reason he turned down top-flight football for another season in the Championship.