Leeds United owner Massimo Cellino has sold 50% of his stake in the club to Italian businessman Andrea Radrizzani.
Radrizzani has purchased his stake through his company Aser Group Holding.
The 42-year-old has been in talks to invest in the Championship club since August 2016, when BBC Sport broke news of his interest.
"I am excited by the challenge ahead and I will work alongside Massimo and everybody at the club to make Leeds as successful as possible," he said.
Cellino took over at Elland Road in April 2014 but the 60-year-old has received three Football Association bans in that time.
In December 2016 he was banned from all football activities for 18 months and fined £250,000 for breaching the FA's football agent rules over the sale of Ross McCormack to Fulham in 2014. He is appealing against the punishment.
Radrizzani, who co-founded sports media agency MP & Silva in 2004, added: "I am fully aware of the great heritage and traditions of Leeds United and I will endeavour to be a fitting custodian on behalf of the many thousands of Leeds supporters, who are the lifeblood of the club.
"I am making a long-term commitment to Leeds United and will work to bring stability through ongoing investment. I aim to bring sustainable growth. I won't do anything that will put the club's future at risk.
"Through working in the sports industry for many years, I have developed a great passion for the English game and I am honoured to have become joint owner of one of the country's biggest clubs.
"I am very impressed with the job [head coach] Garry Monk has done this season and I will do all I can to support him and the team moving forward."
'I needed to bring in a new partner'
Cellino, who had sacked six managers and head coaches before appointing Monk in June, said he felt "that the only way we can get better is for me to bring in a new partner".
The former Cagliari owner added: "Andrea is young and brings a new energy with him, as well as having a good experience in the football media business, which is the future for all clubs.
"I feel that bringing Andrea in as a 50% shareholder to work with me is the best choice we could have made. We will continue building a strong and healthy football club for the future."
Leeds are fifth in the Championship after winning four of their last five matches and seven points off the automatic promotion places.