A federal appeals court in New York confirmed Ulbricht's 2015 conviction and sentence, rejecting his claim of an unfair trial and that being dealt the maximum sentence of life in prison without parole was unreasonably harsh under the law.
The appeals court agreed that the sentence was possibly tougher than the judges might have imposed themselves.
However, they said, based on the crimes and the law, including Ulbricht's attempt to have several people murdered, it was "within the range" of appropriate punishments.
"Ulbricht profited from every sale on Silk Road, and he facilitated the acts of each drug dealer and drug organization that used it," they said.
"Moreover, he attempted to commission at least five murders to protect his criminal enterprise. Those facts render his case distinguishable from those who committed other crimes using Silk Road or otherwise facilitated its operation."
Justice authorities estimated that some $200 million worth of heroin, cocaine and other drugs were exchanged on the site over two years before the FBI shut it down.
Ulbricht himself earned tens of millions of dollars from its operation, much of that seized by US authorities in Bitcoin.
In his 2015 trial, a landmark case in the murky world of online crime, Ulbricht's lawyers had sought to negotiate a 20-year sentence, and government prosecutors had not asked the life-without-parole extreme.
But US District Judge Katherine Forrest gave the harshest punishment possible, telling Ulbricht: "What you did was unprecedented.... You have to pay the consequences."