The 19-year-old has played 19 games in his debut season, averaging 12 disposals and kicking 16 goals.
Thomas was already contracted to 2020, but will now extend his deal until the end of the 2022 campaign.
“I’m really excited about the future with North,” Thomas told North Media.
“I love what this club stands for and what it’s all about, and I can’t wait to be part of what’s to come. We have a great group of young players coming through.
“I’ve really been a part of the club for a few years through the academy, so when I started I was really comfortable and felt like part of the team straight away.
“I’ve loved my first year and have learnt so much. I’m looking forward to getting a full pre-season in and improving next year.”
North Melbourne 2021 Player Movements
Paul Ahern (delisted), Joel Crocker (delisted), Majak Daw (delisted), Sam Durdin (delisted), Lachlan Hosie (delisted), Ben Jacobs (delisted), Jamie Macmillan (delisted), Thomas Murphy (delisted), Jasper Pittard (delisted), Marley Williams (delisted), Mason Wood (delisted)
Tarryn Thomas (2022)
|Off Contract 2020|
Jed Anderson, Ben Brown, Ben Cunnington, Taylor Garner, Kyron Hayden, Red Og Murphy, Bailey Scott, Curtis Taylor, Kayne Turner, Ed Vickers-Willis, Will Walker, Tristan Xerri