Schneider, one of New South Wales' 10 most-wanted fugitives in 2006, was abducted by masked men from his home in the seaside city in 2015.
His naked body was found days later in a jungle grave.
Bagnato, a kickboxer and Schneider's former business partner, was the first defendant.
"The first defendant is found guilty of all charges and according to the criminal code, the penalty is execution for the murder and deprivation of liberty, plus a year in prison for hiding the body," Judge Sirichai Polkarn was quoted by the Australian Broadcasting Corporation as saying.
Tyler Gerard, 22, from the United States, was convicted of deprivation of liberty and sentenced to three years in jail, but his term was reduced to two years for cooperating with authorities.
Bagnato was arrested in Phnom Penh soon after Schneider's body was found. Gerard was detained as he tried to cross from Thailand to Cambodia.
Two witnesses told the court last year that Bagnato was present at the time of the abduction.
The judge said GPS from a car also connected him to the killing.
The Pattaya Mail has reported that the GPS information showed the vehicle was at the Big Buddha Hill burial site two hours after the kidnapping.
The dispute may have been related to drug dealing, police have said.