Fiorentina are determined to hold on to Colombia winger Juan Guillermo Cuadrado, despite interest from Barcelona.
Adil Rami is on the verge of completing his permanent move to AC Milan.
The 21-year-old played 20 times for Danny Lennon's men during a loan spell with the Buddies last season.
Despite offers from several Championship clubs in England, Newton has opted to work under Lennon and his assistant Tommy Craig again.
Newton said: "I had offers from a few clubs in the Championship but I decided to come back to St Mirren, partly because they couldn't guarantee me football.
"At this stage in my career I really need to be playing games, so I think St Mirren are the right club to come back to.
"From the gaffer Danny to his assistant Tommy Craig and the other backroom staff and the lads, they are a great bunch. I really missed that dressing room when I went back to Newcastle in the summer.
"St Mirren gave me my first shot at football and that meant a lot to me, so coming back is best for both parties."