Ballentine earned his Ph.D. at the University of Cambridge in 1992. He went on to hold research positions at the Paul Scherrer Institut, Switzerland, the University of Michigan, and ETH Zurich, Switzerland. From 2001 to 2013, he held positions at the University of Manchester before joining the faculty at the University of Oxford.
Ballentine has held the vice president, president, and past president positions with the European Association of Geochemistry. He is a member of the Board of Governors of the Oxford Museum of Natural History and the American Geophysical Union, as well as a former scientific steering committee member for the Deep Carbon Observatory. In 2008, he won the Geological Society of London Bigsby medal for significant contributions to geology. The AGU chose Ballentine as a Fellow in 2013, and in 2016, he won the Eni Award, given to researchers who make advanced scientific breakthroughs in the field of energy, for "New Frontiers of Hydrocarbons".