The Wizards announced Thursday that the Polish center had signed the deal on the first day permitted under NBA free agency rules.
Gortat posted a picture of himself signing the papers on his Twitter page, writing that it was the "best day of my life!!!"
Gortat agreed to the deal on July 1, reaffirming his desire to remain with the Wizards after helping lead the club to its first playoff berth since 2008.
Gortat averaged 13.2 points and a team-leading 9.5 rebounds after he was acquired in a preseason trade with the Phoenix Suns.
Gortat said feeling appreciated went a long way in helping his time on the free agent market this summer be short and sweet.
The 6-foot-11 center said the "love" he received during a surprise visit to his basketball camp in Poland from a delegation of Wizards executives and coaches prior to the start of free agency was a gesture he didn't forget.
It's why he said he barely spent a day mulling potential offers before agreeing to sign a five-year, $60 million deal to remain in Washington.
Fresh off helping the Wizards reach the playoffs for the first time since, Gortat said he feels like he's found a long-term home, and is anxious to continue playing alongside all-star point guard John Wall and guard Bradley Beal.