Himalayacetus is an extinct genus of carnivorous aquatic mammal of the family Ambulocetidae. The holotype was found in Himachal Pradesh, India, in what was the remnants of the ancient Tethys Ocean during the Early Eocene (Ypresian), 55.8 to 48.6 MYA. This makes Himalayacetus the oldest archaeocete known, extending the fossil record of whales some 3.5 million years.
Himalayacetus lived in the ancient coastline of the ancient Tethys Ocean before the Indian Plate had collided with the Cimmerian coast. Just like Gandakasia, Himalayacetus is only known from a single jaw fragment, making comparisons to other Ambulocetids difficult.