The Hungary international will cost €70 million after Liverpool agreed to trigger his release clause hours before its expiry on June 30.
Newcastle United also held an interest the midfielder but were unable to get a deal over the line due to the finances involved.
Szoboszlai is Liverpool’s second addition of the Premier League transfer window following the earlier arrival of Alexis Mac Allister.
“A really historic club, really good players, good coach, everything is good,” the Hungarian told Liverpool’s official website.
“For me, It was perfect to make the next step in a club like this. The fans, the stadium, everything is really good, I enjoyed the last [few] days and I’m looking forward to knowing everybody better.
“The last three or four days went really long – it was not that easy but in the end, I’m here, I’m happy and I can’t wait to get started.”
Szoboszlai also lauded Jurgen Klopp’s impact on his decision to move to the red half of Merseyside and is looking forward to working under the German.
“As I said, I think in 2020, Klopp is one of the best coaches in the world,” he added.
“How he acts next to the pitch, it is like he plays with the guys – I like that really a lot.
“And also how he has done with the last few years, what he has achieved with this club is also really impressive, so I am looking forward to working with him.”
After Naby Keita’s departure, Szoboszlai will wear the number eight jersey at Anfield and hope to replicate Steven Gerrard’s heroics.
Capable of playing out wide or in midfield, Szoboszlai offers his new employers plenty of tactical flexibility as they look to bounce back from a disappointing season.
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