The 21-year-old Chester born man began his career in Everton's academy, and made one appearance for the Toffees as a 91st-minute substitute in a 2017 Europa League game.
In 2020 he joined Salford and went into their development squad, before going on to make his first team debut later that year.
The England youth international played nine games in total for City – along with six games on loan at Morecambe last season – and has now joined the Saints on a permanent deal.
Saints boss Anthony Limbrick said the club were targeting a defensive midfielder in the window and they've got their man.
He explained: "He is a good young player who has been around Everton and England, and we wanted to strengthen in the holding midfield area and we've done that.
"He's a good character and a good player who needs an opportunity and a home with it.
"It's a permanent deal, and he comes having played a handful of games with Salford.
"He will add to what we have, we have good technical players in midfield such as Routledge, Redmond, Smith and Clarke, and Alex will just bring a defensive side to our options."
And the TNS boss hasn't ruled out further moves in the window.
"We are having a lot of conversations behind the scenes regarding other players," explained Limbrick.
"We want to get the right players in, with the right ability that will not only make the squad strong, but the starting line-up stronger to.
"If there are players available then we will continue that, they have to be a good character to that is really key and you have to get that right."