A letter from former President Joe Biden to President Donald Trump, left in the Oval Office, has been exposed, revealing Mr Biden’s parting words to his successor.

Fox News correspondent Peter Doocy obtained the letter left by the former president, reading it aloud to viewers on air.

Departing presidents leaving letters for their predecessors has become a tradition in the US, observed by most that sit in the Oval Office of the White House.

Know the news with the 7NEWS app: Download today

Mr Doocy told viewers the letter was written in “cursive handwriting”, adding he struggled to read it at times, before sharing its contents “in full” on the news network.

“Dear President Trump. As I take leave of this sacred office I wish you and your family all the best in the next four years,” Mr Doocy said on Fox News.

“The American people — and people around the world — look to this house for steadiness in the inevitable storms of history, and my prayer is that the coming years will be a time of prosperity, peace, and grace for our nation.

“May God bless you and guide you as he has blessed and guided our beloved country since our founding.”

Mr Trump found the letter after being prompted by a journalist during his Oval Office executive order blitz on his inauguration day.

The 47th President of the United States joked that he may not have found the letter for months if he had not been prompted.

Mr Doocy said Mr Trump has shared the letter with him, adding he had given permission for it to be shared with viewers.

“We heard him, last night, describe it as inspirational. And we can confirm the President’s assessment. It is an inspirational, forward-looking well wish, and quite possibly the only time that they will exchange letters ever again,” Mr Doocy said.

Although not all presidential letters have been shared publicly, Mr Biden’s letter to Mr Trump is shorter than other letters that have been shared with the public.

Former President Barack Obama left Mr Trump a lengthy letter to Mr Trump when he left office, writing “This is a unique office, without a clear blueprint for success, so I don’t know that any advice from me will be particularly helpful”, before sharing multiple paragraphs of wisdom and learnings with the Republican.