Hill started his career at First Boston in 1973, where he was one of the founding principals of its mergers and acquisitions department, and then moved to Smith Barney, where he served as the head of its mergers and acquisitions department. In 1982, he joined Lehman Brothers as a partner in its M&A department and later became head of M&A, head of Investment Banking and co-CEO.

BAAM is currently the world's largest discretionary allocator to hedge funds, with Investors including mostly corporate and public pension funds, sovereign wealth funds and central banks. The business's growth from 2007 to 2013, at a time when the industry generally contracted substantially, was featured in a June 2013 Harvard Business Review case study. Hill has appeared at the 2014 Credit Suisse Financial Services Forum, the 2011 Milken Institute Global Conference, and the 2012 Bloomberg Hedge Fund Summit, among others. In 2014, Hill was inducted into Institutional Investor's Alpha's "Hedge Fund Hall of Fame".

In 1993 Hill joined Blackstone, where he served as co-head of the corporate mergers and acquisitions advisory group. In 2007, he became vice chairman of the firm. Since 2000, he has served as President and chief executive of Blackstone's hedge fund Business, Blackstone Alternative Asset Management (BAAM), and has grown that business's assets under management from $1.3 billion in 2000 to $56 billion as of December 31, 2013.

In 2014, the Frick Collection presented "Renaissance and Baroque Bronzes from the Hill Collection", a group of thirty-three statuettes from Hill's personal collection that date from the mid-fifteenth to the eighteenth centuries. In 2017, Hill will open a gallery on West 24th Street in Chelsea to exhibit his private collection.