Sunsundegui initially started out as a rolling stock repair workshop for Renfe, the Spanish state railway company.

[3] In the late 2010s and early 2020s, the Sunsundegui SB3 and SC5 were ordered in large numbers by Bus Éireann, Go-Ahead Ireland and Ulsterbus for intercity bus services on the island of Ireland;[3] Israel also emerged as another strong export market for the company.

[7] Sunsundegui received a loan of €8.9 million from the provincial government of Navarre in May 2022, after struggling through the COVID-19 pandemic due to a reduced demand for new vehicles.

Prior to the pandemic, Sunsundegui employed 550 people; this reduced to 250 employees by March 2022, although plans were in place to begin new recruitments.

[8] Sunsundegui have predominantly produced high-floor coaches throughout their history, diversifying into low-floor city bus models in the late 2010s.