He was speaking at the Munich Security Conference, which was earlier opened by German Chancellor Angela Merkel.
Mr Pence told the conference: "The United States of America strongly supports NATO and will be unwavering in our commitment to this trans-Atlantic alliance.
"We've been faithful for generations, and as you keep faith with us, under President Trump, we will always keep faith with you."
He said that because Mr Trump believes that the protection of freedom is only achieved through strength, the US would be increasing the amount it spends on its military.
Mr Pence's address to the annual gathering of diplomats and security officials was part of an attempt to reassure sceptical allies in Europe about American foreign policy under Mr Trump.
He went on to meet Ms Merkel and was then expected to sit down with leaders from Estonia, Latvia, Lithuania, Ukraine and Turkey.
Earlier, Mrs Merkel said Germany would do "everything possible" to meet the NATO target for spending 2% of GDP on defence by 2024.
The speech and meetings come amid concerns about links between the Trump administration and Russia, and fears about Kremlin aggression.
Mr Pence spelled out the threats to the alliance and the Western world, including to Ukraine, for which he said Russia must be made to honour the Minsk agreement.
He added: "And know this, the United States will continue to hold Russia accountable even as we search for new common ground, which, as you know, President Trump believes can be found."
Russian foreign minister Sergei Lavrov said NATO was still a Cold War organisation, the expansion of which had led to the current "unprecedented" tensions in Europe.
He said a "post-West" world order, with each country defined by their sovereignty and the US and Russia engaged in a "pragmatic" relationship, was the only way to reduce those tensions.
Mr Pence said the other main threats came from Iran, which he said the US would prevent from gaining a nuclear weapon, and Islamic State, which he said would be defeated by a new US plan.