Westland Dairy Company chief executive Toni Brendish will step down on Friday.
The High Court today gave the final consent for Yili to take over the co-op from farmer shareholders for $588m.
The Overseas Investment Office (OIO) gave its blessings to the deal earlier this week.
The High Court decision means Westland shareholders will receive an immediate payment of $3.41/share in the company.
Yili already has a presence in New Zealand, after it acquired Oceania Dairy Group in 2013.
It has since invested approximately $660 million in establishing milk powder, infant formula and UHT production lines for Oceania.
Westland shareholders voted overwhelmingly to accept the Yili offer two weeks ago.