The model was travelling to Los Angeles at the age of 15 to visit her aunt when she eventually decided to stay in the US, reports femalefirst.co.uk.
McConaughey along with their three children Levi, 7, Vida, 5, and Livingston, 2, were present to see Alves get US citizenship.
McConaughey took to Twitter to post a photograph of the family together at the courtroom, and wrote: "Congratulations Camila on getting your US citizenship today - another fellow and great American.(sic)”
Camila also took to Twitter to express her joy and tweeted: "Happy to say I now hold an American passport! I have so much respect and appreciation for this country. #newuscitizen (sic).”