It was the second trial for Sandy Murphy, 32, and Rick Tabish, 39, in Binion's death.
They were convicted of murder in 2000 and faced life in prison, but the Nevada Supreme Court overturned the verdicts in July 2003 and ordered a new trial.
Murphy sobbed when the retrial verdicts were read. Tabish smiled as his lawyers slapped him on the back.
Prosecutors accused Murphy and Tabish of forcing a lethal combination of heroin and the anti-depressant drug Xanax down Binion's throat and suffocating him.
Authorities said the pair then conspired to steal the silver cache that Binion had stored in a vault about 60 miles from Las Vegas.
The defense contended that Binion died of an accidental overdose after two decades of heroin addiction.
The jury, which deliberated fewer than four days, convicted Murphy and Tabish on lesser charges of conspiracy, grand larceny and burglary in connection with the treasure dig.
Clark County District Judge Joseph Bonaventure set sentencing on those charges for January 28. Each could face as many as 16 years in prison, The Associated Press reported.
Binion, 55, was the multimillionaire heir of Benny Binion, founder of the Binion's Horseshoe Hotel & Casino in downtown Las Vegas, a high-stakes gambling venue that plays host to the annual World Series of Poker.
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