Mike Pence's promise follows reports on Wednesday that the American pastor, detained for nearly two years on terror and espionage charges in Turkey, will be placed under house arrest as his trial continues.
Responding to the update, Pence tweeted that both him and Donald Trump "made clear last week and have worked tirelessly for months to free Pastor Andrew Brunson".
He added: "He should have been freed long ago. He's now under house arrest - but we won't stop until he's fully released and reunited with his family, friends and church. #FreeAndrewBrunson."
Mr Pence also threatened Nato ally Turkey with economic sanctions over the issue while speaking at the close of a three-day conference on religious freedom.
He said that if Turkey does not take immediate action to free Brunson "the United States of America will impose severe economic sanctions on Turkey."
Brunson, a 50 year old evangelical pastor from Black Mountain, North Carolina, was arrested in December 2016 and later charged with links to a failed plot to overthrow the Turkish government in July 2016.
Supporters claim he is effectively a political prisoner being held as a bargaining chip by Turkey who is actively seeking the extradition of preacher Fethullah Gülen, which it blames for the failed coup.
Brunson faces up to 15 years in prison for "committing crimes on behalf of terror groups".
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