Mr Biden leads President Donald Trump with 51 per cent of the vote and more than 2.5 million ballots cast.
Arizona has historically been a Republican stronghold, but Biden’s bid to flip the state was boosted by a growing voter-age Latino population and residents moving from California to Arizona.
Arizona is the only state to flip from Republican to Democrat support so far.
Mr Biden has a narrow electoral lead with 238 votes compared to 213 for Mr Trump, both candidates need 270 votes to win.
The election is now pinned on a handful swing states that have yet to declare a winner, Georgia, Michigan, North Carolina, Wisconsin and Pennsylvania.