Speaking to the BBC, Ash Carter said it is an "important part of the deterrent structure of Nato", allowing the UK to punch above its weight.
Read more: Scottish Labour vote not to renew Trident
He added that Trident aids the UK's special relationship with the US, helping the UK to "continue to play that outsized role on the global stage that it does because of its moral stand and its historical standing".
"It's important that the military power matches that standing and so we're very supportive of it."
"We depend upon the United Kingdom, the United Kingdom depends on us, that's part of the special relationship," he said. "We build joint strike fighters together, we build Trident missiles together."
The comments come ahead of an expected vote this year by MPs on whether to back government plans to renew the UK's Trident submarines.
Meanwhile, the Labour party continues to debate whether or not it will officially support the renewal of the nuclear deterrent.