O’Neil began his early career with Halliburton, where he spent 19 years. He held a number of leadership roles within the company, lastly as director of global deep-water development. O’Neil joined Quanta Services, Inc. in 1999 as vice president of operations integration. He held a variety of executive roles throughout his tenure at Quanta, including senior vice president of operations, integration and audit; chief operating officer; chief executive officer; and president.
O’Neil earned a civil engineering degree from Tulane University.