Cairns, 30, scored 28 goals in his first season with the club, helping them earn promotion to the Northern Premier League.
He said: "I missed the club last season and family comes first, but it was an easy decision to come back to the Purps and when I spoke to Robbo, it was all done and dusted in 5 minutes.
“I now can't wait to get started and get back to the lads and the staff and of course the supporters, who were always great with me."
Cairns moved back to Runcorn Town last season to be nearer to home for the birth of his second child, but will now be back in Purple for 2020/21. In three seasons with Runcorn, he has scored 119 goals in 115 appearances.
Manager Craig Robinson told the club’s official website: "To have Craig back with us for the new season is great news and I'm sure it will the fans a big lift in this tough period we are all going through.
“Craig is a natural born goalscorer with a hunger to be successful that matches our clubs'. He showed great desire to come back and it didn't take long to get the deal over the line.
“I’m sure he'll get a big welcome back when we can all return"