"Through these conversations, I feel confident he would help us turn the ideas in this agenda into laws to help improve people's lives. That's why I'll be voting for him this fall," Ryan wrote.
Initially, the speaker, who likes to call himself a "policy guy" and a "movement conservative", did not agree with Trump's positions on key policy planks of mainstream Republicans of the past 40 years, including a free trade agenda and the effort to rein in federal spending on entitlements.
Those issues were the hallmark of Ryan's early congressional career and Trump stands squarely against them.
Additionally, Trump's proposals to ban all Muslim travel into the United States and his campaign's tenor in terms of comments regarding minorities, women and the disabled gave Ryan pause.
Those concerns appear to remain, and Ryan vowed to speak out against the presidential candidate if he crosses lines again.
"It's no secret that he and I have our differences. I won't pretend otherwise. And when I feel the need to, I'll continue to speak my mind. But the reality is, on the issues that make up our agenda, we have more common ground than disagreement," he wrote.