"Bristol and Levi are opening up in the new issue of Us Weekly confirming that they are engaged," said Lindsay Powers, Us Weekly. "Levi proposed two weeks ago."
Palin and her husband, Todd, released a statement saying that as parents, "we obviously want what is best for our children, but Bristol is ultimately in charge of determining what is best for her and her beautiful son."
"Bristol believes in redemption and forgiveness to a degree most of us struggle to put in practice in our daily lives," they said. "We pray that, as a couple, Bristol and Levi's relationship matures into one that will allow Tripp to grow up graced with two loving parents in his life."
Earlier this month, Johnston, 20, acknowledged telling lies about the Palin family after he and Bristol broke up last year. He says he's apologized.
He also posed on the February cover of Playgirl magazine sporting nothing but a sultry gaze.
The couple had been going through an intense custody battle just two months ago. But according to Us Weekly that is no longer an issue.
"Bristol moved out of her parents home to her own condo in Anchorage," said Powers. "They have gotten more accustomed to parenting and as they worked out a custody plan they started spending more time together and realized that they wanted to reunite."
Bristol Palin was thrust into the spotlight as a pregnant teen during her mother's unsuccessful campaign for vice president. She recently signed on with a group to offer speeches on abstinence and "pro-life" issues, among other topics, and will be paid between $15,000 and $30,000 per appearance, Palin family attorney Thomas Van Flein said in May.
The Associated Press contributed to this report.