The 30-year-old re-united with Port`s former manager Alan Lewer and head of development Mark Wright in July, following a previous spell together at Maltese side Floriana.
Roberts (pictured) joined from Welsh Premier side Bangor City after his contract was cancelled after he revealed he wanted to join the Sandgrounders.
He had been with the Citizens since 2016 and also has more 200 Football League appearances to his name.
After making his first appearance for Crewe Alexandra aged 16, he went on to represent England at under-16, 17, 18 and under-19 levels.
Meanwhile, defender Andy White has joined Evo-Stik League Premier side Altrincham on a permanent transfer for an undisclosed fee.
White joined the club at the beginning of the season and has made 19 appearances for Southport in the National League North.