The founder of one of the world's largest private equity firms, Harris and his group paid $320 million to Jeff Vanderbeek for the rights to the Devils and the lease to the Prudential Center.
The deal was announced Thursday morning after the attorneys for the two sides took about 15 extra minutes to sign off on the transfer of the financially strapped three-time Stanley Cup champions.
Harris, whose main partner is fellow equities investor David Blitzer, needed roughly a week to close the deal after talks with Philadelphia attorney Andrew Barroway fell through.
The NHL's board of governors approved the deal Wednesday.
Vanderbeek will remain with the Devils as a senior adviser.