(CNN) -- The man once known as Canada's "prince of pot" is now a federal inmate in the U.S. system after a judge in Washington sentenced him Friday to five years in prison.

Marijuana activist Marc Emery pleaded guilty in May in U.S. District Court in Seattle, Washington, to a single count of conspiracy to manufacture marijuana after an 18-month investigation into the seed-selling business Emery operated from his head shop in Vancouver, British Columbia.

By imposing the five-year sentence, which includes four years of supervised probation, U.S. District Judge Ricardo S. Martinez honored a plea deal that Emery, 52, entered into with U.S. authorities to avoid a lengthier sentence.

"There is no question your actions were illegal and criminal and your actions ensured that others broke the law and suffered the consequences," the judge told Emery during the hearing.

Dozens of Emery's supporters gathered outside Seattle's federal courthouse to protest the sentence, which marks the end of a five-year legal battle against a man once described by U.S. authorities as one of its most wanted international drug trafficking targets -- and the only one from Canada.

Emery is the founder of the British Columbia Marijuana Party and the website CannabisCulture.com. His status in Canada as a tireless advocate for marijuana legalization has been cemented through years of sit-ins, demonstrations and runs for political office. By his own account, he has been arrested at least a dozen times since 1995 related to his activism, and Vancouver police have raided his shop several times since it opened in 1994.

In his plea agreement, Emery admitted to operating a marijuana seed selling business with two co-defendants, who entered pleas this year to lesser offenses and were placed on probation in Canada. He also admitted to selling seeds to customers in the United States through mail and telephone orders and in his Vancouver retail store.

"Marc Emery decided that U.S. laws did not apply to him, but he was wrong," said U.S. Attorney Jenny A. Durkan in a statement Friday. "Emery put his personal profits above the law. He made millions of dollars by shipping millions of seeds into the U.S. He sold to anyone who would pay him -- with no regard for the age or criminal activities of his customers. Now, Emery is paying the price for being part of the illegal drug trade that damages lives, homes and the environment."

But Emery and his supporters worldwide have maintained from the start that his prosecution was politically motivated, citing a 2005 DEA press release touting his arrest as a "significant blow" to the marijuana legalization movement.

"Hundreds of thousands of dollars of Emery's illicit profits are known to have been channeled to marijuana legalization groups active in the United States and Canada. Drug legalization lobbyists have one less pot of money to rely on," former DEA Administrator Karen Tandy said in the July 2005 statement, which can no longer be found on the DEA's website.

iReport: Emery's wife speaks

Emery's lawyer reminded the judge of the press release in his presentencing memorandum, claiming there are other seed selling businesses in Canada that the U.S. government chose not to go after.

"The only thing that makes Mr. Emery unique or different from most of these other seed sellers is that Marc donated his proceeds to help fund lawful marijuana legalization efforts throughout the United States and Canada. On this record, no one can (or should) take the government seriously when it claims that this case was not politically motivated," Richard Troberman wrote.

But the U.S. Attorney's Office said that Emery's personal politics had nothing to do with his prosecution.

"Through the years, and in various contexts, Marc Emery has meant different things to many people. But in the context of this federal criminal prosecution, Emery stands before the court as many others have before him -- as an admitted drug dealer who has entered a plea of guilty to a large scale marijuana trafficking conspiracy," the U.S. attorney's office wrote in its presentencing memo. "The government's case was investigated and prosecuted without regard for Emery's personal politics, his political agenda or the ways in which he chose to spend the proceeds of his drug crimes."

With Emery in prison, his wife, Jodie, has become the face behind their cause, which has not fallen dormant in his absence. Rallies to support Emery and the legalization movement will be held in more than 70 cities across the globe on September 18, she said.

"It's going to be a long, difficult road ahead, but we'll be able to make it with all the support we have," she said.

Emery also remains firm in his beliefs, though in a letter to the court, he admitted his means may have been self-defeating.

"It was my sincere belief that the prohibitions on cannabis are hurtful to U.S. and Canadian citizens and are contrary to the U.S. and Canadian constitutions. I was, however, overzealous and reckless in pursuing this belief, and acted arrogantly in violation of U.S. federal law. I regret not choosing other methods -- legal ones -- to achieve my goals of peaceful political reform."