He has agreed a deal to remain with the Hoppers until the end of the 2020/21 campaign.
Having arrived at the club from Fylde last summer, Arnold led the Hoppers to the North Premier title - and promotion straight back to National League Two North.
Initially Arnold was contracted until the end of upcoming 2018/19 season, but the club has moved quickly to tie him down to a longer deal.
Head of Rugby Operations Gareth Dyer said “We are delighted to have extended Paul’s stay at Lightfoot Green. His impact has been instant, and this signals that we are delighted with the job he has done so far, and it is important to reward that.
"Having our head coach committed for the next three years is important as we make our return to National Two North. We are looking to build a stable playing base at the club and with most of our key players having committed their medium-term futures to the club, it is important we have a stable foundation off the field also.
Arnold said “I am really pleased to be committing myself to the club for the next three seasons. It’s a real family club, a fantastic club with proper rugby people involved throughout. The plans off the field are impressive and I am looking forward to helping us to grow as a club on the field at 1st XV level.
"Joining Hoppers was a fresh start for both parties and myself, Emma and my family have all been made to feel part of the Hoppers family and really enjoyed becoming part of the club.
"We know this season is going to be more difficult at a higher level than last season, but we can’t wait for the season to start. I would like to thank everyone behind the scenes for their continued support and for making my job easier. We are very lucky to have so many committed volunteers at our great club”.