Speaking from England's St George's Park base, Oxlade-Chamberlain said, "I'm delighted to have signed for Liverpool and a big thank you to everyone here at the FA that has made this possible, using the facilities".
The winger could be one of three players that may leave the Emirates this summer.
The Premier League champions had a bid accepted by their London counterparts but the player held out in favour of a preferred move to Anfield.
Oxlade-Chamberlain, who was also wanted by Chelsea, has penned a five-year contract with the Merseyside club.
He will become Liverpool's second most expensive signing after Guinea global Naby Keita, who will join the club from next season after the Reds triggered a £48m release clause in the RB Leipzig midfielder's contract.
Press Association Sport understands the clubs have agreed a deal that will see the England worldwide move to Anfield.
The 24-year-old swapped Arsenal for Liverpool in a £40 million move today.
Oxlade Chamberlain played 198 times for Arsenal since joining them from Southampton in 2011. He is a good player for the squad at this moment, but central midfield, I am still scratching my head on that one.
"We won that game but lost the return match at Arsenal when he started and played well, I think he hit the post".
Before the window closes at 11pm tonight, Liverpool could still seal deals for Southampton centre-back Virgil van Dijk and AS Monaco attacking midfielder Thomas Lemar if they can convince their clubs into selling.
- Malinga to lead Sri Lanka against India
- PSG obligated to pay €180m in Kylian Mbappé loan deal
- Birling Gap Beach: 100 Treated After Chemical 'Mist'
- Netanyahu: Iran wants to use Syria to eradicate Israel
- Federer fit ahead of US
- Burger King launches digital currency WhopperCoin in Russian Federation
- US Urges Myanmar to Avoid Reprisals After Attacks Kill 89
- Transgender troops in military can continue to serve for now, Mattis says
- City make sensational Raheem Sterling offer as makeweight for Arsenal's Alexis Sanchez
- Looking for more assets after finding out Isaiah Thomas injury