The Nuggets had to outbid the Dallas Mavericks to secure Harrington's signature after Dallas followed up its trade acquisition of Tyson Chandler earlier Tuesday with a hard push for Harrington, which included an in-person recruiting pitch at the NBA's annual summer league in Las Vegas from Mavericks owner Mark Cuban.
The former New York Knicks backup tweeted: "I'm taking my Talents to the MILE HIGH."
But Denver would appear to have a greater need for Harrington than Dallas, given that the Nuggets expect to start the season with Kenyon Martin and Chris Andersen unavailable after both recently underwent surgical procedures.
That enabled Harrington's agent, Dan Fegan, to land a deal starting at the full $5.8 million mid-level exception from the Nuggets which extends for the maximum allowed five years.
Buoyed by the acquisition of Chandler after it appeared that Toronto would acquire the 7-footer from Charlotte, Dallas quickly pinpointed Harrington as its next top summer target.
The Mavericks know they need more offensive punch next to Dirk Nowitzki and were drawn to Harrington's scoring ability. Dallas also had more than the usual familiarity with Harrington's game after Mavs coach Rick Carlisle had Harrington in Indiana.
Dallas, though, proved hesitant to extend a full five-year offer because it already has a deep roster and wasn't sure about the minutes allotment it could pledge to Harrington.
The Nuggets made two more moves on Wednesday to solidify their bench. A league source told ESPN.com's John Hollinger that the team has agreed to terms with forward Shelden Williams and guard Anthony Carter and is expected to sign both later in the day. Both deals would be for the league's veteran minimum salary.
The 35-year-old Carter has played 11 seasons, the last four of them with the Nuggets and will serve as the third point guard behind Chauncey Billups and Ty Lawson. Last year he averaged 3.3 points and 3.0 assists.
A four-year veteran, Williams averaged 3.7 points and 2.7 rebounds for Boston last season. He had previously played for Atlanta, Sacramento and Minnesota.
Marc Stein is a senior NBA writer for ESPN.com. ESPN.com's John Hollinger and The Associated Press contributed to this report.