The corpse was found in the former Simpson pub on Romford Road, Forest Gate, at around 3pm on Friday.
Pictures at the scene show a forensics tent outside the building, with officers attending and cordons in place.
A post-mortem is set to take place on October 19.
The body was found during construction work at the site.
A Met Police spokesman said: “Police were called just after 1500hrs on Friday, 15 October, to the former Simpson pub on Romford Road, Forest Gate.
“The premises had been derelict for many years.
“A body was discovered during building work on the site.
“Tests will now be carried out and a post mortem will be held on Tuesday, 19 October to establish further information.”
The pub had been known as The Freemasons Arms before at reopened as Simpsons between the 1980s and 2000s.
Watch the latest videos from Yahoo News UK