Derby County's administrators have exchanged contracts for the sale of the club with Chris Kirchner.
American businessman Kirchner will fund the club from next week and says he does not "anticipate any issues" completing the process of the sale.
In a statement, Quantuma said the exchange was "conditional on the sale of the stadium, EFL approval and receiving secured creditor consent".
Completion of the sale is targeted for 31 May or before that date.
Preferred bidder Kirchner said on Twitter:
"Today is a day I'll never forget. I'm humbled and excited to share that we've exchanged contracts with Quantuma and I will be the next owner of Derby County Football Club.
"My team is now moving forward on the process to rebuild this iconic club. This has been a traumatic period for everyone and I can say that I hope this is the most difficult transaction I have to complete for a very long time."
Quantuma said: "The period of time between exchange and completion will allow the joint administrators and all relevant stakeholders the time required to work together to meet the conditions required to complete this very complex transaction."
Proposed takeovers of the club by Derventio Holdings and Spanish businessman Erik Alonso collapsed last year.
Derby were placed in administration by former owner Mel Morris in September and docked 21 points over the course of the season because of that and breaches of EFL financial rules.
The penalties contributed to the Rams, who are managed by former England striker Wayne Rooney, being relegated from the Championship and into the third tier for the first time since 1986.
Kirchner withdrew from the race to buy the club just before Christmas, but later revived his interest and was named as the preferred bidder on 6 April.
Morris still owns the stadium, but a group involving local businessmen, 'Team Derby' MPs and city council bosses are continuing to work on a deal to purchase it, so the Kirchner takeover can be completed.
Rooney has indicated a willingness to stay despite the club playing in League One next season and him being linked with other jobs.
He has a year remaining on the contract he agreed when he was confirmed in the post in January 2021.
Analysis - BBC Radio Derby's Rams commentator Ed Dawes
This is great news for supporters. The wilderness of missed deadlines had left the fan base in despair.
Chris Kirchner is key to Wayne Rooney's development of Derby County. I expect Rooney to settle his future shortly, and that will open the door to re-signing players who made such great efforts for him this season.
I am aware that several of them have attracted interest from other clubs, but are purely holding out for Rooney to sign a new contract.
Now Kirchner has exchanged contracts, it means Derby can work with a budget and move forward. The club can start planning to hire staff and rebuild the departments savaged by the previous ownership and administration.
They can also agree season ticket prices for League One and put them on sale, which in the closed season is massively important income for the Rams.
The one line of Kirchner and Quantuma's statements that offers a reason for caution is that the deal is conditional on the sale of the stadium.
Once that is done, then the past can finally be consigned to history. Until then it all hinges on Mel Morris agreeing a price that enables him to pay off his debts to Middlesbrough and MSD Holdings. He still holds the key.