A former New Zealand Secondary Schools representative, Thompson will face a tight battle for minutes at hooker with Kereru-Symes and Hastings rake Jacob Devery, who made his Super Rugby debut for the Hurricanes last month.
Magpies head coach Josh Syms said Thompson, whose twin brother Leo made his NRL debut for the Newcastle Knights last weekend, is a valuable addition to what will be a solid-looking squad.
"His style of play will complement both Jacob and Kianu and will provide us with another robust ball carrier where he is lethal with ball in hand."
Hawke's Bay Rugby Union chief executive Jay Campbell said the signing came to fruition after Thompson's agent got in touch late last year.
"His motivation was simply to wear the black and white hoops and to play in front of his whanau and friends," Campbell said.
"It's always brilliant when our home bred players want to return home and its testament to the culture that Josh and his team are creating here that have many reaching out."
The Hawke's Bay Rugby Union have also been boosted by real estate company Ray White taking over as naming rights sponsors of the Nash Cup and Maddison Trophy; the senior Premier men's club competitions.
Premier and Colts rugby both kick off next weekend, with other club grades including a new weight-restricted Under 85kg division starting in April.