Darmian will be on loan until the end of June at which point he will join Inter on a permanent deal with the fee reported to be 2.5 million euros ($2.9 million).
The 30-year-old moved from Torino to Manchester United in 2015 but made little impact at Old Trafford and returned to Italy in 2019 with Parma, making 33 appearances in Serie A last season.
Darmian has 36 caps for the Azzurri and played at the 2014 World Cup but he has been out of favour for the last three years.
The transfer market closes on Monday evening.
