United will receive £600,000 from the Championship club for the Republic Of Ireland U-21 striker, with an additional £250,000 due if they win promotion to the Premiership with Keogh as a player.
"Andy is a player we have been trying to sign for some time," said Moxey.
"We finally reached an agreement with Scunthorpe on Monday and he will begin training on Tuesday morning
"This is an exciting signing for us, at 20-years-old he is a player with bags of potential."
Keogh was coveted by Wolves when he was a schoolboy, but opted to join Leeds United as a youth trainee instead.