The Latics ensured an immediate return to English football's second tier with Saturday's 4-0 win at Blackpool.
Sharpe, 24, who is British football's youngest chairman, had previously said Wigan would "smash" League One.
"We have to do everything to be ready for the Championship but we've started that process as of three months ago," Sharpe told BBC Radio Manchester.
"I knew in my head we were the best team in the league and we would go up.
"Hopefully next season we'll continue the good times. We'll assess things in the summer but I believe in this group of players."
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Wigan, who have lost just once since being beaten at home by Blackpool on 12 December, are all-but champions, having a three-point lead at the top and a significantly superior goal difference compared to second-placed Burton Albion.
Chris McCann scored Wigan's opener and then set Yanic Wildschut up for the first of his two goals before Will Grigg added a fourth to seal promotion in commanding fashion.
"Today I believe we have won the league," said Sharpe, who succeeded his grandfather Dave Whelan as chairman of the then Championship club in March 2015.
"It's unbelievable. It's a special day. It will live long in the memory."
Wigan Athletic have been planning for their Championship return for three months, says chairman David Sharpe.