Murphy was a guest on the CBS News podcast "The Takeout"
and was pressed repeatedly on his presidential ambitions.
"I am not running for president. I am running for re-election to the Senate," Murphy said in a clip published Tuesday.
Asked specifically if he would rule out a bid, Murphy sought to clarify. "Am I ruling it out? Here we go, I'll rule it out for you," he said.
"Really, not running for president?" asked Steve Chaggaris, CBS political director and "Takeout" co-host.
"I'm running for re-election," Murphy answered.
The Connecticut Democrat told CBS that "I have to ask the voters of Connecticut to send me back for a second term in 2018, so that is where all of my focus is."
Murphy served in the House of Representatives for three terms before winning election to retiring Sen. Joe Lieberman's seat in 2012. At age 44, he is one of the youngest members of the US Senate, and has emerged as one of the more visible Democrats in Congress in the wake of the party's sweeping losses in 2016.
Murphy has also made the push for gun control legislation central to his political identity, having confronted the devastating Sandy Hook Elementary School shooting
just weeks after his election in 2012. Amid the spate of shooting tragedies since -- in Charleston, San Bernardino, Orlando and, most recently, Las Vegas -- Murphy has amplified his campaign, repeatedly introducing legislation that would strengthen background checks for gun purchases.
In the wake of the 2016 Pulse nightclub shooting in Orlando that left 49 people dead, Murphy staged a nearly 15-hour filibuster to protest the lack of any serious debate
on the Senate floor over what, if any, gun control measures should be considered following the tragedy.
And after the deadly massacre in Las Vegas earlier this month, Murphy issued a blistering statement,
rebuking his colleagues and saying that "it's time for Congress to get off its ass and do something" about gun violence.
Despite ruling out a 2020 presidential bid, Murphy did tell CBS that he hoped to take part in forming a new generation of Democratic leaders.
"I'm certainly interested in taking part in that exercise, but my focus is fundamentally on the people of Connecticut and asking them for a second term," he said.