The sum they will pay Tottenham for the 25-year-old midfielder remains undisclosed, but Hull have confirmed it is a new record.
Mason will further strengthen their squad following the earlier signing of goalkeeper David Marshall from Cardiff, and becomes the latest to leave White Hart Lane for East Yorkshire, following Tom Huddlestone, Jake Livermore and Michael Dawson.
He has signed a three-year contract after costing the club in excess of the £10million paid to recruit Abel Hernandez in 2014, and told their official website of his arrival: "I can't wait to get started and I see this as a massive opportunity for me.
"I'm delighted and excited to be here."
Mason established himself as a regular starter under Spurs manager Mauricio Pochettino and earned his first and only England cap in the 1-1 draw away to Italy in March 2015
The progress of Dele Alli and Eric Dier last season restricted his first-team chances but he is expected to significantly strengthen Hull's squad.
Before Marshall's arrival, Hull had only 14 fit senior players
Their two new signings, however, combined with six points from three games and the impressive work so far of caretaker manager Mike Phelan has led to optimism they can survive in the Premier League despite their difficult preparations for the season.
"Having spoken to the people up here, I didn't need any convincing," said Marshall
"It's all about having that new, fresh challenge to look forward to
"I feel that this is a club that is going places, especially when you look at the start they have made to the Premier League season
"There are only four or five goalkeepers in this division who can categorically say that they are their club's number one (goalkeeper).
"Of course I anticipate a battle for the jersey
You can't take anything for granted and I'm here to fight for a place."
Source : PA
Source: PA