STV asks voters to rank candidates in order of their preference. A candidate wins when they receive a certain number of votes based on a proportion of the total votes cast.
The system is designed to reflect the preferences of a greater number of voters because second, third and other preferences are taken into account.
All councillors supported the change, with only Mayor John Carter abstaining from the vote. However, he applauded the outcome, saying it was the clear preference of younger councillors.
The council's decision follows a non-binding survey held during July that sought feedback on which system residents and ratepayers preferred.
A total of 637 submissions were received with 406 opting for STV, and 231 preferring to remain with FPP. Of those who preferred STV, 139 said the voting system was "fair" or "fairer", while the majority (79) of those who preferred FPP said it was easy to understand.
The council will reconsider whether to retain STV or return to FPP after the 2025 election.