The Horniman Museum is to reopen from July 30, after warning closure was costing it £150,000 a month.
The charity-run museum, based in Forest Hill, had been closed since March 18, but gardens had remained open to the public since the end of May.
To control crowd numbers and social distancing, free tickets will have to be booked in advance.
“The Horniman is a charity and whilst the Museum is closed we are losing around £150,000 each month,” it said in a statement.
“We are grateful for the generosity of all our donors and members for supporting us during the closure.”
Tickets will be available to book for the museum, which specialises in natural history, anthropology and musical instruments from Monday, July 20.
The gardens are open from 7.15am to sunset, Monday to Saturday, and from 8am on Sunday.
Nearly one million people visited the museum last year, according to the latest stats.