Google’s top cloud-computing executive and one of tech’s highest-ranking women is departing the company after three years and will be succeeded by a former executive of business-software rival Oracle Corp.

Diane Greene will relinquish her role as CEO of Google Cloud in January, she said in a blog post Friday. Thomas Kurian, a former president of product development at Oracle, will then step in. Ms. Greene will retain her seat on the board of Google parent Alphabet Inc.

Ms....