The former chief executive at pharmaceutical giant GlaxoSmithKline, Andrew Witty, has been named chief executive at Optum, the huge and still fast-growing health care services business of UnitedHealth Group.

Witty will step down immediately from the UnitedHealth Group board of directors and succeed Larry Renfro as Optum's leader. Renfro will become managing partner for a series of domestic and international funds called Optum Ventures.

As part of the leadership shuffle announced Tuesday, UnitedHealth Group said that Optum Ventures will now include a new $100 million global fund that's dedicated to emerging technology, data analytics and health care services.

"We are deeply fortunate in Andrew Witty to have the right person to extend Optum's momentum and lead the business in its next phase of growth," David Wichmann, the chief executive at UnitedHealth Group, said in a statement.

One of Optum's primary businesses is pharmaceutical benefits management, which includes negotiating prices with drug companies. Called a PBM, for short, the unit also structures the medication benefit in health plans and creates pharmacy networks. Optum also has a growing division that provides direct patient care, plus a unit for data and analytics.

Witty joined GlaxoSmithKline in 1985 and served as chief executive and a director of the company from 2008 until 2017. He's the outgoing chancellor of the University of Nottingham, a British public research university, and serves on the Singapore Economic Development Board International Advisory Committee.

Witty was knighted in 2012 for services to the U.K. economy, UnitedHealth Group said, adding that the executive serves on the Council at the London School of Hygiene and Tropical Medicine and as an adviser to the Bill and Melinda Gates Foundation.

Optum has 140,000 employees worldwide and had 2017 revenue of $91 billion, including in-house business with other units of UnitedHealth Group.

Renfro has led the unit since 2011. He will remain a vice chairman at UnitedHealth Group and lead enterprise growth efforts, the company said. At Optum Ventures, the new global fund adds to a domestic ventures fund announced in November 2017. Altogether, the funds have total investment commitments of up to $600 million.

"I'm extremely proud of the immense progress made in advancing health care and this enterprise by the people of Optum over the last seven years, and believe strongly Andrew Witty is the right person to lead our well-established, high performing team," Renfro said in a statement.

Witty said in a statement: "In many ways, even with all its accomplishments, Optum feels as though it is just getting started."