Santamaria also paid tribute to his predecessor John Campbell, who is leaving Breakfast after three years for a new role as TVNZ's chief correspondent.
"John, I am so happy for you... this new role is YOU!" he wrote.
"I am honoured to be stepping into your sizeable shoes. And I am thrilled we are colleagues again, 21 years later."
Santamaria, an Auckland-born journalist, started his career as a sports reporter for Newshub before leaving New Zealand to pursue other ventures.
He's been teasing his next steps on Twitter after revealing he was leaving Al Jazeera, where he worked for over 16 years.
Campbell's last day on the Breakfast couch will be this Friday.
Yesterday TVNZ released a statement confirming the news, with Campbell sharing he's "so up for" his new role.
"Being TVNZ's chief correspondent is a new and really exciting broadcast-digital role, and I am so up for it!"
He also added that he's grateful for his time at Breakfast and will dearly miss his co-stars, Clarkson, Stewart and McLean.
"They're wonderful people, and we're friends, and that matters when you're starting work at four am, and doing three hours, live, each morning in their company. I'll miss them, but I'll be back on Breakfast at regular intervals."
He also confirmed the career change on Twitter today, saying he was "kinda busting to work in the field again".
His new role as chief correspondent would see him working on specials and documentaries, he said.
"Campbell will tell stories across TVNZ's news and current affairs shows, on television and digital. He will also host a number of specials," TVNZ said.
TVNZ's head of news and current affairs Paul Yurisich shared a tribute to Campbell who he called the "absolute best" at "telling people's stories".
"He's been a crucial part of the Breakfast team, but we're very excited to have him out and about around Aotearoa getting into the big issues and providing even more depth to our daily coverage," Yurisich said.
