Thames Sports Investment, founded by Russian Anton Zingarevich, agreed to buy a majority stake from long-standing Reading owner John Madejski in January.
"Reading Football Club are pleased to announce that a 51 per cent acquisition by Thames Sports Investment (owned by Anton Zingarevich) has now been completed, complying with all Premier League and Football League requirements," the club said.
"Four additional directors have been added to the Reading Football Club board chaired by Sir John Madejski, namely Anton Zingarevich, Christopher Samuelson, Andrew Obolensky and chief executive Nigel Howe. Ian Wood-Smith also remains a director.
"The football club and TSI would like to thank both the Premier League and Football League for their assistance, and we now enter another bright new era for our historic club, back in the Premier League."
Madejski, who made his money from the Auto Trader magazine, has been chairman of Reading for more than two decades and will remain in that role. He backed a move in 1998 to the club's modern, 25,000-seater stadium that is named after him.