Grundy,who added he didn't want to announce the news during the height of the bushfire disasters,said there was a pull to return home to Adelaide but ultimately the long-term deal got him over the line.
"As I've gotten older,family has become more important to me,"he said.
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"My partner is from Adelaide as well and she's a massive priority in my life as well,so there are a few delicate things outside of just where you enjoy playing football as well.
"I know my mum will be watching,she misses me and wishes I was home. I'm sorry mum. But at the end of the day,we've built a family here and a home here and looking forward to really putting down the roots over the next seven years here and building a life."
The 25-year-old Grundy will be 33 by the time the contract ends but the South Australian-born ruckman has emerged alongside Melbourne's Max Gawn as the game's premier big man.
Seven-year deals have become the new normal for the game's best players,with the Giants'Stephen Coniglio and Richmond's Tom Lynch both signing a seven-year deal in recent seasons.
Grundy said the seven-year deal was"pretty important from my perspective".
Pies star Brodie Grundy has re-signed with the Magpies on a new seven-year deal.Credit:AAP
"Throughout the year I did take my time to explore other possibilities of what that would look like but at the end of the day it always came back to staying at the club,"Grundy said.
"As a player you want to have that long-term security but in terms of also fitting in with the list strategy that Ned[Magpies list manager Ned Guy] is working so hard to try and tick off on,so we had to come to an agreement there and I think both parties are happy."
But the star ruckman,who will put his hand up to represent the All-Stars in next month's bushfire fundraiser,said falling short of premiership success in 2018 wasn't driving him.
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"The four years before that when we weren't playing finals was a pretty dark time to be at the footy club,"he said.
"When I came here as an 18-year-old we were at the peak of our powers and then we went through a bit of a rebuilding phase.
"To see that through and get so close in the grand final loss and prelim,I wouldn't say it's unfinished business but it's staying the course. I'd love to be able to get to the stage where at the end of my career I've had a really profound impact[on and off the field]."