Kimeu began to work in paleoanthropology as a labourer for Louis Leakey and Mary Leakey in the 1950s. He was recruited for Mary Leakey's team when she took over as head of excavations at Olduvai. She preferred to hire Kamba men rather than Kikuyu, whom Louis preferred. In 1963 he joined with Richard Leakey's expeditions, accompanying him to the Omo River and Lake Rudolf (now Lake Turkana) in 1967. 