Trailing 24-15 at the break, Newcastle scored four tries in 18 second-half minutes to turn the game around.
Scrum-half Takulua crossed the line three times and also added another nine points with his boot off the tee.
Northampton, who earned a bonus point of their own with four tries, were undone by a series of defensive and handling errors in the second half.
A second successive home win for Newcastle lifts them above Northampton to seventh and just a point behind sixth-placed Harlequins.
Northampton have now lost their past two Premiership matches to fall to eighth and are without an away win in six games in all competitions.
Jim Mallinder's side made a terrific start with two tries inside the opening five minutes from Ken Pisi and Jamie Gibson.
Harry Mallinder's score in the corner seemingly put them in charge at the break despite Takulua and Sean Robinson crossing for the hosts.
But a lightning restart from Newcastle saw Rob Vickers and a Takulua brace change the complexion of the game within 10 minutes.
Falcons went on to inflict further damage through hooker Kyle Cooper before Mikey Haywood kept Saints in the hunt, although Mark Wilson's late score from a rolling maul settled the affair.
Newcastle: Tait; Goneva, Waldouck, Socino, Sinoti; Hodgson, Takulua; Vickers, Cooper, Welsh, Green, Robinson, Wilson, Welch (capt), Latu.
Replacements: Lawson, Harris, Wilson, Fonua, Olmstead, Egerton, Delany, Watson.
Northampton: Tuala; K. Pisi, Tuitavake, Mallinder, Foden (capt); Myler, Groom; A. Waller, Haywood, Brookes, Ratuniyarawa, Day, Gibson, Clark, Harrison.
Replacements: Clare, E. Waller, Hill, Paterson, Nutley, Dickson, Hutchinson, Pablo Estelles.
For the latest rugby union news follow @bbcrugbyunion on Twitter.
A Sonatane Takulua hat-trick helped Newcastle to an impressive victory against Northampton at Kingston Park.