Press Association Sport understands the deal, which would see striker David Ngog travelling in the opposite direction, has been completed subject to medicals for both players on Wednesday.
The news comes after days of frenzied speculation, with the Reds seemingly determined to get their hands on Henderson before he heads off with the England Under-21s squad for the European Championships in Denmark on Wednesday.
Liverpool, who signed strikers Andy Carroll and Luis Suarez in a massive January spending spree, have wasted little time in trying to implement their summer rebuilding mission.
The Black Cats had insisted - throughout reports of the Merseysiders' interest in their highest-profile academy graduate - that he was simply not for sale.
However, the reality which has long been acknowledged by manager Steve Bruce is that every player has his price and for Henderson, that had been set at around the £20million mark.
Bruce had no desire to sell a player who emerged from the ranks last season to hold down a regular place in his hometown club's first-choice XI. However, as was the case when Aston Villa came calling in January with a deal potentially rising to £24million for Darren Bent, Sunderland were made an offer which represents a significant return on their investment.
If the figures add up favourably, what is not in dispute is that Henderson's departure will leave another major hole in Bruce's squad.
His form suffered in the immediate aftermath of his senior England debut against France in November last year, but the 20-year-old has been a key man for the Black Cats in the last two seasons and will take some replacing.
The manager is already engaged in an extensive recruitment drive with Bent yet to be replaced, while the returns of loan signings Danny Welbeck, Nedum Onuoha, John Mensah and Sulley Muntari to their clubs has left him with a series of sizeable gaps to plug.
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