Liverpool announced the news on Thursday, with Robertson's contract expiring this summer. He joined from Hull City in 2017 for just £8 million — a fee that looks more remarkable with every passing year.
In nine seasons he made 373 appearances, won two Premier League titles, the Champions League, the FA Cup, two League Cups, the Club World Cup, the UEFA Super Cup and the Community Shield.
Liverpool called him a "genuine Liverpool legend." Robertson, typically, was more modest about it.
"I'll let other people say if I'm a Liverpool legend or not," he said. "But from minute one I came into this football club, I wanted to be successful. I wanted to try to bring trophies back to this football club."
He was measured but emotional in reflecting on the departure.
"It's never easy leaving a club like Liverpool. It has been a huge part of mine and my family's life for the last nine years. But for me, players move on, other people move on — the thing that stays the same is the club and obviously the fans."
Robertson admitted he had chances to go before now.
"I've had opportunities to leave and I've not taken them because of how difficult it is to leave this club. And I wouldn't change that for the world."
"But I know football moves on, I know teams move on and I think now is the time for me to move on and go wherever my next move is and wherever my career takes me."
His exit follows Mohamed Salah's confirmed departure and is the latest step in the gradual dismantling of Jürgen Klopp's great side. Trent Alexander-Arnold left for Real Madrid last summer. Luís Díaz moved to Bayern Munich. Diogo Jota passed away. Robertson is next.
He lost his starting place this season after the £40 million arrival of Milos Kerkez from Bournemouth, making just six Premier League starts. Tottenham tried to sign him in January for £5 million — a deal that fell through when Liverpool could not recall Kostas Tsimikas from his loan at Roma.
Atlético Madrid, Napoli, Juventus and Saudi clubs are expected to pursue him as a free agent.
Robertson still has games to play at Anfield. The farewells can wait.
"The time to have the emotional farewell and tell the fans what they mean to me — that will come closer to the end. I don't think I'm quite ready for that yet."