The 25-year-old striker ended his first season at Wetherby Road as the club's leading goal-scorer after netting 14 times and is now set to remain with the League Two Sulphurites for the foreseeable future.
The ex-Middlesbrough forward's form in front of goal reportedly made him the subject of interest from Stockport County during the January transfer window, though Town boss Simon Weaver insisted at the time that he had no intention of selling one of his best players, and has now managed to tie his man down until 2025.
Armstrong, however, did not need too much persuading to stick around.
“When I first signed here last year I knew it was somewhere I wanted to tie myself down to for a long time so I’m over the moon that the gaffer has shown his faith in me and offered me a long-term contract," he said.
“We want to show what we can do again like we did at the start of last season, we want to be up there challenging and trying to get out of this league and into League One which we are capable of doing.
“Personally I want to do better than last season and get back to the form I showed in the first half of the season.
“Myself and the team had started off really well and I had never felt more at home at a club.
“Even through the tough times we had towards the end of last season I still realty enjoyed playing which is a rarity, the lads here are great and the gaffer believed in me throughout, so it was a no-brainer to sign again.”
Armstrong joined Harrogate from League Two rivals Salford City last summer having spent part of the 2020/21 season on loan with Hartlepool United in the National League.
He had previously turned out for Middlesbrough, Cowdenbeath, Blyth Spartans and Accrington Stanley.