The 18-year-old became the first-ever female or male qualifier to win a major tournament, triumphing 6-4 6-3 over fellow debutant finalist Leylah Fernandez at Flushing Meadows.
Raducanu did not drop a set throughout the tournament on her way to victory in only her second career grand slam after reaching the fourth round at Wimbledon earlier this year.
The achievement by Raducanu, who is the youngest women's grand slam finalist since a 17-year-old Maria Sharapova won at Wimbledon in 2004, was labeled as "remarkable" by the Queen.
"I send my congratulations to you on your success in winning the United States Open Tennis Championships," the Queen's message to Raducanu said.
"It is a remarkable achievement at such a young age, and is a testament to your hard work and dedication.
"I have no doubt your outstanding performance, and that of your opponent Leylah Fernandez, will inspire the next generation of tennis players. I send my warmest good wishes to you and your many supporters."
The Duke and Duchess of Cambridge also offered their congratulations along with United Kingdom Prime Minister Boris Johnson who praised the British sensation on social media.
"You showed extraordinary skill, poise and guts and we are all hugely proud of you," Mr Johnson wrote.
There were further tributes on social media coming from musicians Liam Gallagher and the Spice Girls, as well as football identities Marcus Rashford and Gary Lineker.