Whitfield also makes Giants history by becoming the first player to win two best and fairests, following his 2018 gong.
"Nick has been a stalwart of our backline for years now and has always been incredibly highly valued internally with two top-five finishes before this year. He's once again taken his game to another level this year and thoroughly deserves the accolades that have come his way," Giants coach Leon Cameron said.
"Taking on an official leadership role ahead of this season shows his development off the field and on the field, we saw Lachie continue to show his class and work-rate across the entire season."