The Oscar-winning playboy, 52, popped the question to the British lawyer, 36, sometime in the past two weeks, a source tells Us.
On April 23, the twosome were spotted dining together at Craig's restaurant in West Hollywood—and, according to one onlooker "they were toasting the engagement." The infamous Hollywood bachelor even told a fellow diner that they were engaged, the witness claims.
"This is the healthiest relationship I've ever seen George in," a source recently told Us. "He seems incredibly happy, and Amal is such a sweet and intelligent girl, who has her own thoughts and ideas and doesn't just bow down to everything he says."
The pair were first spotted out together in October 2013 in London, while he was still dating model Monika Jakisic. They later attended a White House screening of Monuments Men as a couple.
In mid-March the duo vacationed in South Africa, where they were photographed strolling the beach together.
Clooney was previously married to actress Talia Balsam in 1989 before divorcing in 1993. He has had lengthy romances with British model Lisa Snowdon, Italian actress Elisabetta Canalis, and former professional wrestler and model Stacy Keibler, whom he split from in 2013 after two years of dating. Kiebler got married to tech entrepreneur Jared Pobre in March and announced her first pregnancy soon after.
Though he's held several longterm relationships, marriage has been off the table following his 1993 divorce.
In 2011, he told Piers Morgan, "I was married, so I gave it a shot," which he said should have "proven how good I was at it."
Entertainment Tonight was first to speculate the news. Clooney's rep had no comment.
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!