The 23-year-old midfielder penned a two-year contract until summer 2022, with an option to extend for another year.
Both parties agreed not to disclose the terms of the deal for Duah, who still had a contract with FC Wil 1900 until 2021.
The 23-year-old began his career at BSC Young Boys, where he went through the youth system and played first-team football for the Yellow and Blacks 13 times in the 2016/17 season.
The Swiss-born Ghanaian later had spells at Neuchâtel Xamax, Winterthur and Servette, before joining FC FC Wil 1900 permanently in the summer of 2019.
At Wilern Duah was used in 33 of the 36 Challenge League games last season. The former Swiss junior international (up to U20 level) scored 12 goals and made 5 assists.