The TV operator recorded a full-year net loss of $607.8 million on revenue that fell 6.8 per cent to $795 million.
Its second-half dividend was axed but total subscriber numbers increased as streaming gains outweighed satellite customer losses - but with the company making less money per sub.
Martin Stewart, Sky's chief executive, said the new name would kick in for the second half of the Black Caps' summer cricket season.
"We will work together with the Sky Stadium team to deliver outstanding fan experiences, with innovations both in the stadium and across all screens. It's all part of our strategy to deepen our connection with sports fans and to work with our sport partners to increase fan engagement.
"We'll be there for the finale of the coming cricket season and the opening of Super Rugby. We can't wait," Stewart said.
Wellington Regional Stadium Trust chief executive Shane Harmon said: "We are thrilled to welcome Sky as our naming rights partner as we move into our third decade.
"Sky is a great fit because of their position as the nation's premium provider and our aligned goals of creating memorable and rewarding experiences," he said.
"Over the past 20 years we have welcomed over 10 million fans and become New Zealand's busiest multi-purpose stadium.
"We look forward to a new era for the stadium where we will work with Sky to deliver world-class events and fan engagement".
Harmon said that the stadium's relationship with Westpac was one of the longest-running in New Zealand sport.
"Westpac has played a critical role in the success of the venue. We have thoroughly enjoyed working with Westpac over the past two decades, developing the partnership at both the local and national level".