A passer-by found the man, who has not been named but was in his 30s, off Promenade Street in Heywood at about 23:25 GMT on Thursday.
He was pronounced dead at the scene and officers are treating the death as suspicious.
A post-mortem examination is due to take place and officers have asked for any witnesses to contact them.
Police have launched an investigation after the body of man was found in an alleyway in Rochdale.