The club confirmed the transfer via Twitter:
In an accompanying article on their official website, the centre-back expressed his delight at joining such an illustrious football club:
I am very happy to sign for Chelsea, a world-famous club with a reputation for major success. I am delighted to be in the Premier League, the best league in the world, and can't wait to meet my team-mates and get going.
I am still at the beginning of my career but I believe this is the place to develop and learn from some of the best players in the world.
Jurgen Klinsmann, manager of the U.S. men's national football team, believes the move is great for Miazga's development, per U.S. Soccer's official Twitter account:
The 20-year-old U.S. star has joined the Blues but could eventually be loaned out to gain first-team experience. Yet a decision on Miazga's immediate future won't be made for a while, as Sports Illustrated's Grant Wahl has detailed:
Dominic Fifield of the Guardian previously wrote how Chelsea had provided assurances they won't loan Miazga out immediately. Fifield also stated how the towering, 6'4" centre-back owns a Polish passport, which means he won't require a work permit.
The west London club's recommendation to sign Miazga may have come from former Premier League pair Steven Gerrard and longtime Blues striker Didier Drogba, according to Sami Mokbel of MailOnline: "It is believed they have alerted clubs in England to his promise."
Last season's Premier League champions have been only too happy to take advantage of the sought-after defender having just one year remaining on his Red Bulls contract.
The Blues certainly need another promising, young defender to potentially partner gifted Frenchman Kurt Zouma. Options alongside Zouma are ageing and struggling for form. However, Bleacher Report's Garry Hayes feels as though the new signing will need time before making appearances in the first team:
Skipper John Terry is 35, while 30-year-old Gary Cahill has even indicated a willingness to leave the club rather than remain on the bench, per Duncan Wright of the Sun.
Miazga is a youngster with a burgeoning reputation and plenty of potential. His development will have to be monitored carefully by a club desperately in need of refreshing the defensive ranks.