The deal will see Kearney, 46, remain in the role for six seasons, joining Ivan Cleary (2006-2011) as the longest-serving head coach in the club's history.
"Securing Stephen for another three years is a huge boost for us," Warriors chief executive Cameron George said.
"We haven't enjoyed a lot of stability as an organisation, especially in the coaching area. Without stability in our football department it's extremely challenging to improve and to achieve continuity," he said.
