Jeff, who is the world's wealthiest man, has yet to sign the pledge.
MacKenzie announced on Saturday that she had joined the Giving Pledge, an initiative started by Warren Buffett and Bill and Melinda Gates, which encourages billionaires to donate half of their fortune. MacKenzie is worth about $37 billion following her divorce. Jeff, who is the world's wealthiest man with a net worth of $114 billion, has not yet signed the pledge, but praised his ex's decision on Twitter on Tuesday.
"MacKenzie is going to be amazing and thoughtful and effective at philanthropy, and I'm proud of her," he wrote alongside MacKenzie's letter announcing her commitment. "Her letter is so beautiful. Go get ‘em MacKenzie."
The letter focused on MacKenzie's desire to give back. "I have no doubt that tremendous value comes when people act quickly on the impulse to give. No drive has more positive ripple effects than the desire to be of service," she wrote.
"We each come by the gifts we have to offer by an infinite series of influences and lucky breaks we can never fully understand. In addition to whatever assets life has nurtured in me, I have a disproportionate amount of money to share," she continued. "My approach to philanthropy will continue to be thoughtful. It will take time and effort and care. But I won’t wait. And I will keep at it until the safe is empty."
Jeff and MacKenzie were married for 25 years before announcing their split in January. They revealed in April that they had settled their divorce. MacKenzie shared the terms of their agreement on Twitter at the time, stating that Jeff is retaining 75 percent of the former couple's Amazon shares (about 12 percent of the company). The shares she's keeping give her roughly four percent of the company.
"Excited about my own plans. Grateful for the past as I look forward to what comes next," MacKenzie's statement read.