New director Sue Ireland will take over the reins at the City of London Corporation's (CLC's) open spaces department, which has a £20m annual budget and employs more than 300 staff.
Ireland will join the CLC on 14 April from Chelmsford Borough Council, where she is the director of parks and heritage services.
"I'm very excited as the City of London has heritage and green space in abundance," said Ireland.
"The number of staff is more of a step up than the budget - it's a substantially bigger job covering a larger area. While it is a large budget, money everywhere is tight and we have to look very carefully at how it's being spent to make the best use of it."
Ireland will be responsible for the 4,330ha of parks and open spaces owned and managed by the CLC, including Hampstead Heath, Epping Forest and Burnham Beeches, as well as more than 150 gardens, parks, churchyards and plazas across the Square Mile alone.
Current director Jennifer Adams will spend a fortnight introducing Ireland to the role before she retires after seven years in the post.
Parks consultant Sid Sullivan said it was reassuring that the CLC had appointed someone with such a well-recognised background.
"It's the premier position and it's in a league of its own, along with Royal Parks, so it's important the person appointed had the ability to deal with that," he said.
"The economy is beginning to slow down and as that happens there's pressure on costs but I think Sue Ireland has the skills to deal with that."