Grenier will replace Steve Neff, who is retiring at the end of the first quarter of 2020.

Grenier will run a division that has repositioned its most popular mutual funds, such as Contrafund, to be less expensive when held in corporate 401(k) plans, to counter an industry-wide problem of heavy withdrawals from actively managed funds.

Meanwhile, Boston-based Fidelity has fully embraced passive index funds, a necessary move after watching Vanguard Group gobble up market share with its emphasis on low costs over the past decade.

Grenier was not available for an interview, a Fidelity spokesman said.

Neff, a 23-year veteran of Fidelity, has run Boston-based Fidelity's asset management arm for less than a year. When he replaced Charles Morrison, the move underscored the growing importance of data systems for fund companies. Neff was head of technology and global services before taking the asset management position.

Fidelity said it was Neff's personal decision to retire. He helped the asset management arm migrate systems to the cloud and advanced the use of artificial intelligence and machine learning, the company said.

Fidelity funds have collected $87 billion in net deposits over the 12-month period that ended Oct. 31, driven by passively managed funds. The Fidelity 500 Index Fund, for example, collected $32.4 billion in net deposits during the period for total assets of $215 billion, according to mutual fund research firm Morningstar.

Still, Vanguard's mutual fund market share has increased 1 percentage point over the past 12 months to 25.6%, Morningstar said. That is slightly more than the combined market share of its three biggest rivals, Fidelity, American Funds and BlackRock Inc.

Fidelity's most popular mutual funds, meanwhile, have experienced billions of dollars in net withdrawals. The total, however, is somewhat misleading because billions of dollars of assets also have been shifted into collective investment trusts, or CITs.

Fidelity Contrafund, for example, has more than $29 billion in a CIT structure, which mirrors the larger $120 billion mutual fund in terms of holdings and management, but offers lower fees and overhead costs because it is not regulated by the U.S. Securities and Exchange Commission.

For the past two years, Grenier has served as global head of asset management at Fidelity International Ltd in London. The company is not owned by Boston-based Fidelity, but has common owners that include the family of Fidelity Investments Chair Abigail Johnson.

“Bart is the ideal candidate to succeed Steve," Johnson said in a memo to employees. "The breadth of his experience across investment strategies and asset classes, as well as his strategic insights and spirit of innovation, makes him well suited to lead asset management.”

In 2008, Grenier was charged by the Securities and Exchange Commission along with 12 other Fidelity employees and former employees for improperly accepting $1.6 million in travel, entertainment and other gifts paid for by outside brokers hoping to win business from asset managers.

Grenier oversaw Fidelity’s equity trading desk and up to eight other business groups. He worked at Fidelity from 1991 to 2005 before leaving to join DB Advisors, a division of Deutsche Asset Management. He rejoined Fidelity in 2017 and then took his current job in London.

Grenier settled the SEC case without admitting or denying the allegations. He also agreed to pay about $26,000 in disgorgement and prejudgment interest to the U.S. Treasury, according to the SEC.

By Tim McLaughlin