It was a triumphant return for the Australian to the US capital, where he lifted the men's singles trophy in 2019 for his last ATP Tour title then tumbled out in the first round of last year's tournament.
Kyrgios, who lost to Novak Djokovic in four sets at the All England Club last month, took just 81 minutes to defeat his Japanese opponent Yoshihito Nishioka 6-4 6-3.
A short time later he returned to Stadium Court at Rock Creek Park Tennis Centre to help American Jack Sock defeat the fourth-seeded duo of Ivan Dodig and Austin Krajicek 7-5 6-4.
In singles, the 27-year-old dropped just one set in five matches, never had his serve broken and led the tournament with 96 aces, including 12 against Nishioka.
"It's just very emotional for me," Kyrgios said after the singles final.
"To see where I was at last year to now, it's just an incredible transformation. I just came out with great energy. I knew that I had experience on my side today. I love this court, I've played so many good matches here, so I'm just really happy with myself.
"I've been in some really dark places. Just to be able to turn it around… There are so many people who have helped me get there, but myself, I've shown some serious strength to just continue and persevere and get through all those times and be able to still perform and win tournaments like this one."
The Canberra product appears on track to gain singles seeding for the US Open, which begins in New York on August 29. The DC victory takes him to 37 in the world, with the top 32 largely protected from facing a top opponent in the first round in Queens.
He will next face Argentina's Sebastian Baez in the first round of the Montreal Open, but expressed his gratitude to Washington before leaving the city.
"What an amazing day," he said in a video posted to social media.
"Thank you so much to the city of Washington, the Washington fans, you guys are amazing and I can't wait to see you guys next year."