Dobbin, 23, spent last season on loan at Championship side Preston North End and scored in both league games against Saints.
The wide man netted another nine goals to reach a tally of 11, and registered eight assists, across 41 appearances in all competitions.
Having come through the Everton academy, Dobbin made 20 senior appearances for the Toffees, as well as spending a season on loan at Derby County in League One, before a permanent switch to Aston Villa in 2024.
"What a finish"
Lewis Dobbin with a fantastic solo goal for Preston at Deepdale 🪄 pic.twitter.com/NuUaDcjmtr
— Sky Sports Football (@SkyFootball) September 13, 2025
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The 23 year old hasn't made an appearance for the Villans and has spent the past two years on loan at West Brom, Norwich City, and Preston.
Saints have now agreed a deal with Aston Villa to bring the left-sided winger, who can also play up front, to St Mary's on a permanent basis.
The deal is expected to be completed within the next few days.
It was reported that the south coast outfit had joined the race for Dobbin's signature alongside league rivals, including Middlesbrough and Wolves.
Preston were also keen to bring their former loanee back to Deepdale, but were seemingly priced out of a move.
Dobbin will become Saints' fourth addition of the summer after ex-loanees Daniel Peretz, Cyle Larin and George Long all signed permanent deals.