He left the Reds in summer 2017 to sign for MK Dons.
After 18 months with MK Dons he signed for Dundee United in January 2019, where he made 110 appearances.
Pawlett only made 13 appearances in the current campaign.
Dundee United captain Ryan Edwards, Liam Smith and Ian Harkes will also leave.
Meanwhile, loanees Jamie McGrath (Wigan Athletic) and Loick Ayina (Huddersfield Town) will return to their parent clubs.
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Former Aberdeen midfielder Peter Pawlett to leave relegated Dundee United
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