Senator Rand Paul's nearly 13 hour filibuster may have started a conversation about U.S. drone policy, but it didn't stop John Brennan from becoming CIA director.

Senators voted to 63 - 34 to elevate President Obama's top counter-terrorism adviser at the White House to lead the Central Intelligence Agency after Paul, R-Ky., dropped his opposition to a vote Thursday afternoon.

Paul had mounted the filibuster because he wanted assurances that the government would not target a non-combatant American citizen in the U.S. under the secret legal justification it uses to kill suspected terrorists overseas with armed drone strikes.

Related: Rand Paul Wins Praise From GOP and Liberals

Those assurances came from Attorney General Eric Holder on Thursday in the form of a one line letter.

"It has come to my attention that you have now asked an additional question: 'Does the President have the authority to use a weaponized drone to kill an American not engaged in combat on American soil?'" wrote Holder. "The answer to that question is no."

After that letter was produced, Paul voted with 85 other senators to end debate. Paul later opposed Brennan's nomination. But his filibuster did have an effect. Senate Minority Leader Mitch McConnell, who had appeared ready to allow Brennan's nomination to proceed on Wednesday, was among 16 Republicans who opposed cutting off debate on Thursday. McConnell also opposed Brennan's nomination.

CIA Director nominee John Brennan testifies on Capitol Hill in Washington, Feb. 7, 2013, during his confirmation hearing before the Senate Intelligence Committee. (Manuel Balce Ceneta/AP Photo)

Democrats Patrick Leahy of Vermont and Jeff Merkley of Oregon opposed Brennan along with Independent Bernie Sanders of Vermont.

Related: Eric Holder's Letter to Rand Paul

Paul appeared for the first time on the Senate floor since he concluded his marathon filibuster of John Brennan that went from Wednesay into Thursday morning, said he was "very pleased" to get a response to his questions from Holder and he believes the "entire battle was worthwhile."

"It's taken awhile but we got an explicit answer," Paul said this afternoon. "I'm pleased what we did and to me I think the entire battle was worthwhile."

Paul read Holder's letter on the floor of the Senate and said his filibuster was successful not only because it got an answer to a specific question but it also led to a discussion over the use of drones in the nation.

Related: McCain and Graham Blast 'Ridiculous' Filibuster

"I consider it to be our duty to stand up and fight for something that we all believe in and that's the protections that the bill of rights are yours. When you are accused of something you get your day in court," Paul said. "So I am very pleased to have gotten his response back from the Attorney General of the United States."

Paul said he hopes Americans will "see this battle that we've had in the last 24 hours as something that is good for the country."

Read More: John Brennan

From ABC's Z. Byron Wolf and Sunlen Miller