Under a plea bargain, Daniel Biechele, 29, will serve no more than 10 years in prison.
The Feb. 20, 2003, blaze killed 100 people and injured more than 200 others. It was the fourth-deadliest nightclub fire in U.S. history.
Biechele set off a flashy pyrotechnics display during a concert at the West Warwick club called the Station. The sparks ignited flammable soundproofing foam inside the club, fueling a fast-moving fire that quickly enveloped the one-story wooden building and trapped concertgoers.
Biechele pleaded guilty to 100 counts that accused him of lighting the pyrotechnics without the required permit, resulting in the deaths. An additional 100 counts will be dismissed, sparing Biechele what could have been many more years behind bars.
Some relatives of those killed in the fire have criticized the plea agreement, saying they wanted Biechele to stand trial.
Brothers Jeffrey and Michael Derderian, who owned the club,each of involuntary manslaughter. They are accused of installing the flammable soundproofing foam in violation of the state fire code. They have pleaded not guilty.
Biechele has said through his lawyer that he had permission to light the pyrotechnics during the Feb. 20, 2003, concert, but the Derderians have disputed that.
The three defendants were charged with two counts of involuntary manslaughter for each of the 100 people killed. One count per death alleged criminal negligence, the other accused the defendants of committing underlying offenses that led to the deaths.
The night of the fire, hundreds of fans gathered to see Great White, a hard rock band that emerged from the 1980s Los Angeles metal scene with hits including "Once Bitten, Twice Shy" and "Rock Me." Prosecutors claimed in court documents last year that the club was overcrowded that night with 458 people.
As the band took the stage and started performing its first song, giant pyrotechnic sparklers began shooting up, igniting foam that covered the club's walls and ceiling.
Within minutes, the entire club was engulfed in flames and dense smoke filtered through the building, prompting a panicked rush toward the door.
While some escaped through broken windows and many people were able to leave by the front door, a crush of concertgoers became piled up and trapped at the entrance of the club. Most of the bodies were found near the front exit.