HITC Sport understands the Newcastle youngster has agreed a loan move to Blackpool.
Longstaff is highly-regarded at Newcastle after coming through the club's ranks and he was recently handed a new deal at St James' Park.
Longstaff is still well down the pecking order in Rafa Benitez's first-team plans and the club feel he would benefit by going out on loan again next season rather than playing in the club's Under-23s.
Newcastle United manager Rafa Benitez
The 19-year-old spent the second half of last season on loan at Scottish Premiership side Kilmarnock and he helped them avoid relegation.
Longstaff impressing during his loan at Rugby Park, scoring three goals in 17 appearances and they were keen to sign him again this summer.
A number of clubs have enquired about taking Longstaff on loan this summer, but Blackpool have moved quickly to secure the talented midfielder.
Blackpool manager Gary Bowyer
Blackpool boss Gary Bowyer is a big fan of Longstaff and sees him playing a key role in his side as he prepares the club for life back in League One next season.
Longstaff is set to move to Bloomfield Road on an initial six-month loan deal and Newcastle will consider their options on what to do with the player in January.