"I have decided that I am not going to run for president in 2016," Ryan said in a phone interview, noting that he is "at peace" with the decision he made "weeks ago" to forgo a bid for the White House.
"It is amazing the amount of encouragement I have gotten from people—from friends and supporters—but I feel like I am in a position to make a big difference where I am and I want to do that," he said.
The nine-term congressman believes he can make that "big difference" in his new role as chairman of the influential House Ways and Means Committee rather than as a presidential contender.
The committee will meet Tuesday to kick off the new Congress. By announcing that he'll pass on a White House run, Ryan hopes to demonstrate that he'll devote his "undivided attention" to the committee, although he admits that it will be "bittersweet not being on the trail" as a candidate this upcoming cycle.
Ryan, who is married with three young children, said he reached his decision over the holidays last year, well before Friday's news that his former running mate, Mitt Romney, is once again eyeing a presidential bid.
"It is no secret that I have always thought Mitt would make a great president," he said. "As for his plans for 2016, I don't know what he is ultimately going to do and the last thing I want to do is get ahead of his own decision making process."
The congressman would not throw his support behind any potential 2016 presidential candidate during the interview, saying that any endorsement would be "premature."
But, Ryan added, he believes that a Republican can "absolutely" win.