Paul, the last remaining challenger to presumptive nominee Mitt Romney, was able to secure 21 of the 24 delegates from Maine, according to a report from The Associated Press.
Paul finished a close second to former Massachusetts Gov. Mitt Romney in the state's caucuses in February, after a contested process.
Paul's campaign had expected to win Maine, but a snowstorm during the weeklong caucuses led to some counties postponing their votes and Maine GOP Chairman Charlie Webster declaring Romney the winner.
Votes from the delayed counties were finally tallied, but Romney held on to a 156-vote victory.
Romney holds 847 delegates to Paul's 80, according to a tally from The Associated Press, and having all but officially clinched the nomination, has already pivoted to the general election, focusing his attacks on President Obama.
Paul, though, has given no indication that he will drop out prior to the convention in Tampa, Fla., in August and has continued to buy ad time ahead of his home-state primary in Texas.