Reid, 27, will link up with the Highwaymen for their debut season in the EVO-STIK League Premier Division.
He said: “I feel like this club has ambition and a drive for success. Being a part of that sounds exciting.”
Reid scored 66 times for Blyth in 187 appearances, playing for them in National League North last season.
Morpeth chairman Ken Beattie said: “This is a real statement of intent on our part and we are delighted Sean has joined us.
“We’ve moved quickly to bring in a top-quality player who can add goals to a side which already has a fantastic scoring record.
“We’re confident he will be a valuable addition to the squad and one that can help us achieve our ambitions in the Evo-Stik Premier Division.”
Assistant manager Jon McDonald said the club was quick to act when they heard a deal could be possible.
“Sean is a player we have admired for some time,” he said.
“As soon as we learned Sean might be available, we didn’t hesitate. This represents an excellent signing.”