The 22-year-old building monitor pepper-sprayed and tackled the gunman Thursday afternoon in Seattle Pacific University's Otto Miller Hall, likely preventing further carnage, according to police and university officials.
Meis and other students subdued him until officers arrived and handcuffed him moments later.
Police said the shooter, who killed a 19-year-old man and wounded two other young people, had additional rounds and a knife.
"I'm proud of the selfless actions that my roommate, Jon Meis, showed today taking down the shooter," fellow student Matt Garcia wrote on Twitter. "He is a hero."
Meis, a dean's list electrical engineering student, was emotionally anguished but not injured in the shooting, Harborview Medical Center spokeswoman Susan Gregg said Friday. He was treated and released from the hospital.
The leafy campus of the small, private, Christian university about 10 minutes north of downtown Seattle was quiet the morning after the shooting, with a service held at midday. Flowers and candles were laid on the street near Otto Miller Hall, which was taped off as a crime scene. People stopped by the makeshift memorial to pay their respects, and some students milled about or prayed in groups.
The man arrested in the shooting, Aaron R. Ybarra, 26, was booked into the King County Jail late Thursday for investigation of homicide, according to police and the jail roster. He was scheduled to make an initial appearance in a jail courtroom Friday afternoon.
Ybarra was hospitalized for mental health evaluations twice in recent years, said Pete Caw, assistant police chief in Ybarra's hometown, the Seattle suburb of Mountlake Terrace.
Officers encountered Ybarra in 2010 and 2012. Both times, he was severely intoxicated and taken to Swedish Hospital in Edmonds for evaluation, Caw said. In the October 2012 incident, police found Ybarra lying in a roadway.
He was arrested on suspicion of DUI in nearby Edmonds in 2012, said Edmonds police Sgt. Mark Marsh.
"We just hope he's safe," the suspect's father, Ambrose Ybarra, told The Seattle Times on Thursday. "It's upsetting to have these accusations thrown around. We're in emergency mode. We are trying to stay calm."
A woman who answered a cellphone listing for Ybarra's mother, Janice, declined to comment, saying "I will be speaking later."
Ybarra is not a student at the school, police said.
Investigators searched a house in the north Seattle suburb of Mountlake Terrace believed to be tied to Ybarra late Thursday.
The victims included a critically wounded 19-year-old woman who remained in intensive care Friday after a five-hour surgery, as well as 24-year-old man in satisfactory condition, Gregg said. Their identities had not been released.
Meis, who graduated from Seattle Christian Schools in SeaTac, kept a low profile the day after the shooting. An outgoing voice message at a phone listing for his parents' home in Renton said, "We ask that you please respect our privacy during this time while we recover." It solicited prayers for students and the family of the man killed.
Salomon Meza Tapia, a friend who serves with Meis on the board of a student engineers group, described him as a hardworking student who is "always super chill."
"I am not surprised he was cool and collected enough to take action," he wrote in an email to the AP. "I was in the building, and I can say he definitely saved our lives. I am thankful to be alive and thank God for Jon Meis' courage and actions."
Garcia declined to comment in an email to the AP Friday out of respect for his roommate's privacy.
Another roommate, Ryan Salgado, on Thursday gave The Seattle Times a detailed account of what happened, as relayed to him by Meis. Salgado said Meis seemed to be in shock afterward.
Meis typically carries pepper spray with him wherever he goes, because he likes to be prepared, Salgado said.
"There are a number of heroes in this," Assistant Police Chief Paul McDonagh said Thursday. "The people around (the gunman) stepped up."
He added: "But for the great response by the people of Seattle Pacific, this incident might have been much more tragic."
The Seattle Times said Zack McKinley, a friend of Ybarra, described him as "super happy and friendly."
McKinley said the attack was puzzling because Ybarra was happy to have just started a job bagging groceries. Ybarra could get emotionally low but had a good group of friends, McKinley said.
Student Chris Howard was at Otto Miller Hall when the shooting happened. He said he saw the wounded woman on the floor. Her phone was covered in blood, but she asked those helping her to look through her phone for her mother, aunt and best friend.
"She was panicking," Howard said. "She said, 'I think I'm going to die.'"
Howard said he also saw the suspect pinned on the floor.
"The suspect was calm. Not speaking. Not moving. Not struggling. Just there," Howard said.
The shooting came a week before the end of the school year.
McDonagh said detectives are working to figure out the gunman's motive or intended target.
On Thursday evening, an overflow crowd packed the First Free Methodist Church on campus for a service of prayers and song.
"We're a community that relies on Jesus Christ for strength, and we'll need that at this point in time," said Daniel Martin, university president.
The violence follows a spate of recent shootings on or near college campuses.
Last month, Elliot Rodger killed six people and injured seven before turning his gun on himself in a rampage in Isla Vista, California, near two universities, according to police.
Associated Press writers Rachel La Corte in Olympia and Manuel Valdes and Donna Gordon Blankinship in Seattle contributed to this report, along with AP news researcher Rhonda Shafner in New York.