"He was a really bright light in our family, and we've lost a really great guy," the actress, 53, said of her Glee costar, who died last weekend at age 31.
Lynch said Monteith was always grateful for having been given the chance to act on Glee, and he shared that good fortune with others.
"He was always aware that it was a gift," she said. "And he was quite generous and one of those adventurous types of people. I always admired how he would get up and fly to Mexico. He'd throw parties for his friends."
She added: "I don't think he left one day unlived."
Asked how she would want people to remember Monteith, Lynch mentioned his generous spirit.
"He once flew across the country on his own nickel to meet with a sick kid whose last wish was to meet him," she said. "That's the kind of guy he was. He was just a real giver."
Monteith, who had battled addiction throughout his life, was found dead in a Vancouver hotel room on Saturday. Authorities say he died of a "mixed drug toxicity" of heroin and alcohol.
Fans of Monteith's may make donations in his name to three charities that were especially important to him: Project Limelight Society, which exposes youth living in Vancouver's Downtown Eastside to the arts; Virgin Unite, founded to support entrepreneurial efforts to better the world; and Chrysalis, which helps homeless and low-income individuals find employment.