"We're not going to be confirming a judge to the Supreme Court under this president," McConnell told Chuck Todd on NBC's Meet the Press on Sunday morning.
The Republican senator from Kentucky said even if Hillary Clinton is elected in November, the Senate won't consider Obama's nominee.
McConnell echoed and defended his pledge on a variety of network news programs.
"The president nominates. The Senate confirms," McConnell told "Fox News Sunday."
"The American people should have a voice, not this lame duck president out the door," he continued. "All we are doing is following the long-standing tradition of not fulfilling a nomination in the middle of a presidential year."
McConnell said he and his Republican colleagues are unconcerned with the prospect of a more liberal judge nominated by Clinton -- should she emerge victorious in the fall.
"It'd be hard to be more liberal than Merrick Garland, but it's my hope that she will not be making the appointment," McConnell said.
Senate Minority Leader Harry Reid, D-Nev., also appeared on "Meet the Press." Reid predicted McConnell would begin losing support among his fellow Republicans.
"His Republican senators are not going to go over that cliff with him," Reid said. "They're not going to do it. As I told Merrick Garland, 'This is going to break. You're going to become a Supreme Court justice.'"