The final sale price of $467 million is made up of an underlying price of $426m and a $41m payment for estimated working capital.
The working capital value does not include "accounts payable as at completion", which will be retained by Trustpower.
After settling all working capital balances Trustpower expects to receive net proceeds from sale between $432m to $442m.
Details of Manawa's full-year results are due out on May 16.
Mercury said the combined business will have about 787,000 connections, creating New Zealand's leading multi-product utilities retail business.
Chief executive Vince Hawksworth said the acquisition would enable Mercury to accelerate its retail strategy, delivering the right product mix and enhanced value for customers on a faster trajectory.
"Going from a dual utility provider to a truly multi-product retailer adds material value for our customers in terms of convenience, cost efficiencies and the delivery of innovative and exciting products," Hawksworth said.
"Multi-product bundling is a market where Trustpower has had great success and we know nearly half of Mercury customers like the idea of having a single utility provider," he said.
Mercury initially announced it had entered into binding agreements with Trustpower to acquire its retail business in June last year.
The transaction was conditional on several matters, including Commerce Commission clearance, completion of the proposed restructure of Tauranga Energy Consumer Trust and Trustpower shareholder approval.
