HKS produced the original designs for the 71,000-capacity arena which were rejected by co-owners Tom Hicks and George Gillett late last year when they ran £50million over budget.
But after revising those plans, and beating off Manchester-based AFL's rival bid, the American company will get the contract for the new ground.
The announcement on Friday over the stadium's future comes ahead of confirmation that the refinancing of the club owners' loan deal has also been agreed.
The refinancing will mean the American duo have a firm stranglehold on the club, despite opposition from fans' groups, and they are likely to sanction the permanent transfer of on-loan Javier Mascherano as soon as the
£9million transfer of Mohamed Sissoko to Juventus has been agreed.
Hicks and Gillett are trying to re-establish their fractured relationship with the Anfield support and, by allowing manager Rafael Benitez the funds to buy £17million-rated Mascherano they are also intimating the Spaniard has a
long-term future at the club.
But for now the stadium decision is the first step towards settling the crisis that has engulfed the club.
Hicks told the club's website: "HKS has developed a more efficient design that, at the same time, is just as stunning as its original design.
"Liverpool supporters should have high expectations for the future: a premier sporting experience at their new stadium at Stanley Park and a winning club on the pitch for years to come."
Liverpool still insist that the new stadium will open in 2011, and its centrepiece will be an 18,500 new Kop, an increase on the current Kop of 5,000 extra seats.
Laing O'Rourke, the largest privately-owned construction firm in the UK, has also been appointed.