Ysgol Bro Teifi, Llandysul, replaces Ysgol Dyffryn Teifi secondary school and Aberbanc, Coed y Bryn, Pontsian and Llandysul primary schools.
The £25m building has 60 reception and nursery places, 360 primary places and 678 secondary places.
Education Secretary Kirsty Williams will open it on Thursday.
She said: "An integrated, focused school like this is more akin to a smartphone. The school and community can connect, collaborate, and create."
Wales' first purpose-built combined primary and secondary Welsh-medium school will be officially opened in Ceredigion.