The 19-year-old, who has been involved in the first-team squad for 19 games in all competitions so far this season, has made two Premier League appearances from the bench.
Murphy, primarily a centre-back but also capable of playing on the left, made his debut in November’s 4-1 victory at home to Chelsea.
The Republic of Ireland youth international joined the Magpies’ Academy from hometown club Galway United in July 2022 and has now extended his stay with Eddie Howe’s side.
Murphy told newcastleunited.com: “I’m absolutely delighted to sign a new deal here and secure my future with the club.
“I’ve loved every minute since I first signed nearly two years ago. I’ve been fortunate to work with some brilliant players and coaches - with both the Academy and the first team - and I’m really grateful for the opportunities that have come my way.
“It’s an exciting time to be a young player at this club - we can all see there is a pathway from the number of players who have made their first-team debuts this season. I just need to keep working hard and hopefully I can build on the progress I’ve made so far.”
Head coach Eddie Howe said: “I’m really pleased to see Alex sign a new long-term contract here. It’s welldeserved recognition for the work he’s put in over the course of the season.
“He had a great pre-season in America and has gone from strength to strength since, earning himself a Premier League debut and a regular place in our matchday squads.
“We rate Alex highly - he applies himself brilliantly every day and he knows if he continues working hard that further opportunities will come his way.”
Academy Director Steve Harper added: “Everyone at the Academy is delighted to see the progress Alex has made and this contract is a fitting reward for his attitude and hard work.
“Identifying Alex’s potential was excellent work by our recruitment team. His development since joining, initially with the under-21 group and subsequently within the first-team environment, demonstrates the pathway that exists here at Newcastle United.”
