The centre-back, 26, is out of contract in the League Two club in the end of the month.
A club source has advised Soccer Insider Plymouth have taken benefit of Scarr's accessibility by agreeing provisions after he admitted their contract deal.
The deal is anticipated to be completed imminently.
Scarr began 34 of Walsall's league matches last year as they hauled themselves clear of the relegation zone.
Scarr's career began with playing non-league soccer with Causeway United, Redditch United and Stourbridge part-time whilst working in a fitness center.
After impressing at the tier, Scarr went on trial using numerous EFL clubs.
These comprised West Brom and Birmingham City, the team he supports.
He made 22 appearances for Wycombe throughout the 2017/18 season.
Then he combined Walsall in January 2019 and is now a significant member of the group.
So far, he's made 96 appearances in all competitions for the Saddlers.
Argyle finished 18th at the newly concluded League One year.
They narrowly avoided relegation in their very first year back at the next tier of English soccer.
In other news, Tottenham's new appointment is set to promote a fan favorite player.