Gardner, 47, said 17 years at the City Paper — including 10 as the editor — was simply enough time to be in one place.
Gardner, who studied English at the University of Tennessee and Towson University, began his tenure at City Paper as its music editor. He followed that with a year as arts editor before succeeding Andy Markowitz as the paper's editor in 2002.
"He's been a fixture around here for the past 17 years," said City Paper publisher Jennifer Marsh. "It's going to be pretty tough to fill his shoes." The search is on for a new editor, she said.
Gardner's last day will be April 27; his final project, he said, would be putting together the paper's annual guide to the Maryland Film Festival.
An alt-weekly "needs to renew itself every now and then," Gardner said. "Now's as good a time as any.
"There's no way that I'd not want to see it continue to evolve and change and thrive," he added. "I want only the best for this paper and the people who work here."
At the Chronicle, Gardner said, he will be responsible for the publication's finance and policy sections.
"After many years of doing the same thing, a fresh challenge is just as exciting as any part of the change," he said.
A native of Tennessee, Gardner lives in Baltimore's Govans neighborhood with his wife, Courtney, and their two sons, Will and Charlie. He has no plans to move to D.C., Gardner said.
"I'm interested in Baltimore's film scene and music," he said. "Just changing what I do during the day isn't going to change any of that."