It is the 29-year-old's first game back for the County having spent the past two months on international duty, and he will now skipper the team for the remainder of the Championship campaign, as well as in the Royal London One Day Cup.
Young steps into the role at Northants having enjoyed success as a captain in his homeland, leading Central Districts to trophies in the one day Ford Trophy and four-day Plunket Shield during his three years in charge.
And Sadler felt the opening batter was the obvious choice once it became clear that Vasconcelos wanted to step back.
"It all unfolded quite quickly really after last week's win down at Kent," said the head coach.
"Youngy has the full respect of the dressing room, and he is the right man.
"He is in a good place in his career right now and he is ready to do it.
"He has done the job before so he knows what captaincy entails and the added responsibility it brings, and he is excited for the challenge.
"He feels like the first half of the season he was here with us, he got to know the lads pretty well, he got to know their games, he knows conditions.
"And he says he is excited about taking over the captaincy and moving us forward.
"We are delighted Youngy has accepted the role, Vasco is in absolute full support of him, and I am sure it will work well."
Expanding on the fact that Young is taking over a team he has already played with for six weeks, Sadler added: "It is important to get to know the lads and to understand their personalities behind the scenes as well.
"And that's not only from a cricketing perspective, but from them as people, Young knows them.
"He is excited about the captaincy and trying to do the best he can on the pitch."
For the Lancashire game that starts on Tuesday, Young is one of two changes to the Northants squad that won in such dramatic fashion against Kent at Canterbury last week.
Young replaces fellow Kiwi Jimmy Neesham, while James Sales is added to the group.
As for Lancashire, India all-rounder Washington Sundar is set to make his Lancashire debut against Northants after he was named in Glen Chapple's 13-man squad.
England pace bowler Jimmy Anderson will not be involved, but his international team-mate Matt Parkinson returns to the Lancashire four-day squad.
Play starts at the County Ground at 11am on Tuesday, but will finish at the earlier time of 4.30pm, with each of the day's three sessions cut short by 30 minutes due to the warnings of 'extreme heat' in Northampton.
Northants squad v Lancashire: Young (c), Cobb, Gay, Keogh, Kerrigan, McManus (wk), Procter, Rickelton, Sales, Sanderson, Taylor, Vasconcelos, J White
Lancashire squad v Northants: Vilas (c, wk), Bailey, Balderson, Bohannon, Croft, Jennings, Jones, Morley, Parkinson, Sundar, Wells, Williams, Wood