And the boss has backed the talented young fly-half to go on to be the natural successor to Wales star Dan Biggar.
Grayson was the match-winning hero for Saints at the Stoop last Saturday as he held his nerve to slot a tricky conversion in the final minute of the game.
It earned the black, green and gold a precious 20-19 victory against Gallagher Premiership top-four rivals Harlequins and displayed the ability of Grayson.
The 20-year-old had come on for injury victim Piers Francis four minutes into the second half, putting in a big shift at full-back.
Grayson made a try-saving tackle on Marcus Smith before serving up some late heroics with the boot, following Alex Mitchell's eye-catching try.
And Boyd said: "Jimmy's got plenty of chat so he wouldn't have wanted to miss that because he might have got a bit back.
"He's a good, young prospect and he's done a good job for us in Dan's absence.
"He's got a good head on him and he's serving a good apprenticeship under the tutelage of (attack coach) Sam Vesty and Dan Biggar.
"By the time it's Dan's turn to leave Northampton, I'm pretty certain James Grayson can play a lot of games for Saints in the future."
Saints were forced into several back-line reshuffles at the Stoop, with Francis and Ahsee Tuala forced off during the second half.
And Boyd said: "It was an interesting discussion in the box.
"With 20 minutes to go, we'd already lost Piers Francis and we thought we were going to have to take Dan Biggar off, which would have meant putting Jamie Gibson on the wing or one of the half-backs.
"Dan said he could play but he couldn't kick the ball because he had an Achilles issue and he was playing on one leg.
"When Ace Tuala got cramp he was gone so we decided to put Cobus (Reinach) on the wing with Alex Mitchell into nine and the young fella scored a try, with the other young fella (Grayson) able to slot it between the posts by about 20 centimetres."