The 28-year-old was on the verge of staying in the Premier League with Luton Town, but a temporary move to Kenilworth Road collapsed last week as both parties failed to reach a full agreement.
Hayden spent last season on loan at Championship club Norwich City, making just 14 league appearances due to injury, and he will now spend the 2023-24 campaign with Standard Liege.
"Isaac is a quality player with physical impact and leadership," Standard Liege director of football Fergal Harkin told the club's official website.
"He will also bring his wealth of experience on the Premier League pitch to his new teammates and I am convinced that he will help us a lot this season."
Hayden joined Newcastle from Arsenal in 2016 and has since made a total of 171 appearances for the Magpies in all tournaments, scoring seven goals and registering 10 assists.
However, the midfielder is now deemed surplus to requirements under head coach Eddie Howe, and he will look to reignite his career in the prime years of his career in the Belgian Pro League.
Hayden could make his debut for Standard Liege, who are managed by former Celtic boss Ronny Deila, when they take on Eupen after the international break on September 17.
Monaco 
Stade Brestois 29 
Bordeaux 
Nimes 
Bayern Munich 
FC Augsburg 
Paris Saint Germain 
Toulouse 
CSKA Moscow 
FC Rostov 
Leicester 
Chelsea 
Valencia 
Betis 
Dynamo Kyiv 
Chornomorets Odesa 
Verona 
Inter 
Bayer Leverkusen 
FC Heidenheim 
Borussia Dortmund 
SC Freiburg 
VFL Wolfsburg 
Union Berlin 
Arsenal 
Nottingham Forest 
Everton 
Brentford 
Spartak Moscow 
Lokomotiv Moscow 
Rangers 
Dundee Utd 
Atletico Madrid 
Alaves 
Lens 
Marseille 
Ingulets Petrove 
Shakhtar Donetsk 
AC Milan 
Juventus 
ST Malo 
Manchester City 
Tottenham 
Eintracht Frankfurt 
Werder Bremen 
Girona 
Espanyol 
Feyenoord 
Heerenveen 
ST Etienne 
Montpellier 
Grenoble Foot 38 
Heart Of Midlothian 
Celtic 
Reims 
Lyon 
PSV 
Groningen