Kirk Thompson, 46, who played a major role in the response to the bird flu outbreak while he worked at the Department for Environment Food and Rural Affairs (Defra), then left the body under a duvet and had sex with another man.
During the incident he is said to have burnt and cut David Kochs, 43, after they had made contact on the internet.
Newcastle Crown Court heard both men had been taking the drug crystal meth when they engaged in the violent episode at Thompson's flat in the city's Jesmond area in March last year.
At some point during the evening, Thompson, a former altar boy, became aware that Mr Kochs was either dead or unconscious, and he covered him with a duvet on the floor.
He then had sex with another man as the body of Mr Kochs lay in the flat.
The next morning, Mr Thompson messaged his father who on arriving at the flat called the police.
The jury found him guilty of the manslaughter charge as well as one of actual bodily harm.
Mr Justice Globe said sentencing would take place today and told Thompson that a sentence of imprisonment was the only one that he should expect.
He moved to Defra, in Whitehall, in 2003 and during the 2004-5 bird flu scare worked on guidelines on how to deal with the threat.