The 30-year-old moves to The City Ground from fellow Championship side Bournemouth, having been on loan at Fulham last season and helping them to promotion to the Premier League.
Arter was part of the Bournemouth side which rose from League One to the Premier League, featuring on a regular basis in two promotion-winning sides after making his debut in 2010 and going on to rack up over 250 appearances for The Cherries.
The Republic of Ireland international has made close to 100 appearances in the Premier League and now moves to The City Ground.