According to multiple outlets including the BBC, the two clubs came to an agreement on Wednesday evening (30 August) over a transfer worth a total of £40m ($51.7m). That came after Oxlade-Chamberlain's management company appeared to confirm the deal in a tweet that was hastily deleted.
The 24-year-old will now look to quickly agree personal terms on a reported six-year contract and is set to undergo a medical at St George's Park, where he is currently training with the rest of Gareth Southgate's England squad ahead of the forthcoming 2018 World Cup qualifying double-header against Malta and Slovakia.
Chelsea had settled on a £35m price for Oxlade-Chamberlain earlier this week, only for the player, who is looking to feature more regularly in a natural midfield role after being frequently deployed as a wing-back by Arsene Wenger, to rebuff those advances and apparently indicate a preference for a switch to Anfield.
Oxlade-Chamberlain, who joined Arsenal from Southampton as a highly-rated teenager six years ago, has entered the final 12 months of his current contract and supposedly rejected the chance to sign a lucrative £180,000-a-week extension while informing the club of his wish to seek pastures new.
He still started all of the Gunners' opening three matches of the 2017-18 campaign despite the lingering uncertainty over his future and hardly impressed on what now looks almost certainly to have been the last of his 198 appearances in an Arsenal shirt - an embarrassing 4-0 mauling at Liverpool in which he was substituted just past the hour mark.
Wenger had previously been absolutely convinced that Oxlade-Chamberlain would stay at the Emirates Stadium, stating a firm belief that the former Saints prodigy will be "one of the big English players in the coming years". His exit comes at a time of apparent crisis for the club, who are attempting to fend off advances from Manchester City for another more influential contract rebel in Alexis Sanchez.
Oxlade-Chamberlain will follow Mohamed Salah, Dominic Solanke and Andrew Robertson as Liverpool's fourth signing of the current transfer window, with RB Leipzig midfielder Naby Keita also having agreed to join next summer for a club-record fee of approximately £51m.
That latest arrival will seemingly not put an end to their pursuit of Thomas Lemar, contrary to previous reports, with Goal claiming that the Reds, who have also not given up hope of enticing stubborn Southampton into parting company with centre-back Virgil van Dijk before 23.00 BST on Thursday, are continuing discussions with AS Monaco over a deal that could be valued at more than £70m including add-ons.
Arsenal have also been heavily linked with the versatile French international, only for Wenger to declare the pursuit "dead" last week due to Monaco's refusal to sell.