The legal firm was named as the Lancashire club's main sponsors on Tuesday by delighted officials at Haig Avenue.
Commercial and community director Haydn Preece said: "Southport Football Club are delighted to have Kirwans Solicitors as our new shirt sponsors. We are all looking forward to a fantastic season in the Vanarama National League which will include featuring on a weekly BT Sports highlights show every Sunday.
“Kirwans' Lisa Alty has put the sponsorship partnership together as the relationship between the club and Kirwans has developed over a couple of seasons. We look forward to working with Kirwans on their extensive charity and community initiatives."
Defender Josh Thompson at Celtic
David Kirwan, senior partner at Kirwans, said: "We are delighted to be a sponsor of Southport FC and proud to be part of a football club that plays such an integral role in the community.
"We are excited to see where this season will lead and wish the Sandgrounders the very best of luck for the 2015/16 campaign.”
* Southport's defence has been given a major pre-season boost with the signing of Canadian keeper Jonathan Viscosi, former Celtic and Tranmore Rovers centre back Josh Thompson and the return of left-back Will Beesley from a hip injury.
Viscosi, 23, who has played for Brackley Town, Carlton Town and Tiverton Town, and has been watched by AFC Wimbledon, Oldham Athletic and Carlisle United, turned out on one occasion for Chester last season.
In 2013, the 6ft 2ins shot-stopper from Ottawa represented Canada at the World University Games in Kazan, Russia. He also spent four years playing in the United States, where he captained the University of Buffalo side in National Collegiate Athletic Association Division One.
Thompson, 24, signed for manager Paul Carden this week after impressing in a pre-season friendly against Everton. The defender has told the club's fans he turned down approaches from several other clubs because he was so impressed with the set-up at Haig Avenue.
A delighted Carden said: "All three signings will add depth and quality to my squad. Both Jon and Will have worked very hard in pre-season and have shown real hunger and desire while Josh has chosen to join us after several close-season offers."