Talib Sheikh, who jointly runs a range of funds at JP Morgan Asset Management, has resigned after 20 years at the company.
He worked on both open and closed ended funds at JP Morgan, including the £958m Global Macro Opportunities fund.
JP Morgan said Mr Sheikh, who is a managing director at the company, is leaving to pursue other opportunities.
Just last month Mr Sheikh was named lead manager of the JP Morgan Multi-Asset investment trust.
He was previously a portfolio manager in the derivatives implementation team.
The company said existing portfolio managers Michael Schoenhaut and Eric Bernbaum will continue to manage the Global Income fund and the JP Morgan Global Income Conservative fund.
Eric Bernbaum will be added as co-portfolio manager on the Multi-Asset Income fund, alongside existing portfolio manager Michael Schoenhaut.
Existing portfolio managers James Elliot and Shrenick Shah will continue to manage Global Macro Opportunities fund and Global Macro fund.
Gareth Witcomb will continue to manage the Global Balanced fund. Katy Thorneycroft and Jonathan Cummings will be added as co-portfolio managers.
JP Morgan added that current portfolio managers James Elliot and Gareth Witcomb will continue to manage the JP Morgan Investment Funds.