The couple began dating in 2007 and have a 3-year-old son and nearly 2-year-old daughter.
People.com said McConaughey announced his engagement on his WhoSay account Sunday and posted a picture of him kissing his new fiancee in front of a Christmas tree.
"Just asked camila to marry me," he said in his message. "Merry Christmas."
Swim Week Miami Beach 2014 [PHOTOS]