The 24-year-old, who rejected a move to Chelsea on Tuesday after a fee had been agreed, will join Liverpool on a five-year contract worth £120,000 a week.
Oxlade-Chamberlain, who is in the final year of his Arsenal contract, rejected a new deal worth up to £180,000 a week to stay at the Emirates.
He has started each of Arsenal's four games so far this season.
The midfielder is expected to have a medical before flying to Malta with England on Thursday, before the summer transfer window closes at 23:00 BST.
Oxlade-Chamberlain has made 198 appearances for Arsenal since joining them from Southampton in August 2011, scoring 20 goals.
The fee is the highest Liverpool have yet paid for a player - although it will be surpassed by the £48m the Reds have agreed to pay for RB Leipzig's Naby Keita next summer.
So far this summer, Liverpool have signed winger Mohamed Salah from Roma for £34m, full-back Andrew Robertson from Hull for £8m and striker Dominic Solanke after his contract at Chelsea expired.
Liverpool have also been pursuing Monaco's £75m-rated winger Thomas Lemar and Southampton centre-back Virgil van Dijk, while the Reds' Brazil forward Philippe Coutinho remains Barcelona's number one transfer target.
Belgium striker Divock Origi could leave Anfield and join Bundesliga side Wolfsburg on loan before the transfer window closes on Thursday, says BBC Sport's chief football writer Phil McNulty.
The 22-year-old is highly rated by Reds manager Jurgen Klopp but the imminent arrival of Oxlade-Chamberlain from Arsenal means his chances in attack are likely to be restricted this season.
Origi wants regular football throughout Belgium's build-up to next summer's World Cup and Liverpool will also be eager to see the talented young forward continue his progress, so it is expected he will leave Anfield before the deadline.
But what do we know, the transfer season is always filled with numerous surprises.