Ackermann has made just 168 runs across 10 innings this summer and has been replaced as four-day captain, though will continue in his role as T20 captain.
Parkinson was Leicestershire’s leading wicket-taker in 2021 and has chipped in with the bat from the lower order this year; only openers Hassan Azad and Sam Evans have scored more runs than him in 2022.
“It is a huge honour to be appointed four-day captain and I’m incredibly grateful to the club for placing that faith in me,” Parkinson said. “Personally, I feel I have matured massively over recent seasons and developed into a player that can help guide the club to success.
“I have learned so much from Colin during my time as vice-captain. I will continue to lean on him for advice, whilst implementing my own ideas and direction to win matches for Leicestershire.”
Claude Henderson, Leicestershire’s director of cricket, said: “Firstly, we want to thank Ackers for leading the team with great pride and honour throughout his time as four-day captain. He did a fantastic job and will continue to be a massive player for Leicestershire moving forward, where he will remain as our T20 captain.
“We have decided that now is the right time for a change and recognised Callum’s qualities are ideally suited to leading the team in four-day cricket for the remainder of the season. Callum has been an inspiring voice in the changing room, and he commands huge respect through the way he approaches his cricket. We have full belief that he is the right man to take up the role.”