The singer was announced as the new boss of England's Doncaster Rovers club on Thursday (19Jun14) after his takeover bid with former chairman John Ryan was finally accepted.
The deal was completed just weeks after Tomlinson was caught up in a drug scandal last month (May14) when a leaked video appeared to show him smoking marijuana with bandmate Zayn Malik.
Tomlinson has now acknowledged he needs to grow up and change his behaviour so he can be taken seriously as a businessman.
He tells Britain's The Sun newspaper, "I have to mature a little bit... This is life-changing for me. I'm going to have to start acting dead serious... I can't be a big kid anymore or play pranks. I am absolutely going to be very involved in the club.
"I will be committing a lot of time to it. I've said that I want to be across absolutely everything... I guess am a businessman now.
"I know there will be a few eyebrows raised about me doing this. But hopefully the results go a certain way and we'll create a successful club."
Tomlinson follows in the footsteps of Sir Elton John, who became the boss of the Watford soccer team in 1976, and he hopes to get tips from the pop veteran, saying, "I had thought about seeking his advice - but how on earth do you get in touch with Elton John? I don't know. Hopefully this will send the message out!"