The four will be responsible for commissioning content and multi-platform digital services for the Channel under the leadership of S4C's Director of Content, Dafydd Rhys.
Sioned Roberts, Llion Iwan, Gwawr Lloyd and Gaynor Davies join S4C on initial 3 year contracts.
The four will be responsible for different aspects of commissioning for the programme service.
In addition and following internal reorganisation, Geraint Rowlands will take responsibility for some aspects of commissioning and managing certain teams within the Commissioning Directorate as Head of Broadcasting
The appointments are part of S4C's new commissioning strategy announced recently. S4C will move from a system of commissioning decisions being made jointly by the entire commissioning team to a structure where individual commissioners will commission content.
Ian Jones, S4C's Chief Executive, said, "I am delighted to welcome the four Content Commissioners to the new commissioning team. I believe this team has the talent, vision and experience to deliver an exciting, innovative programme schedule which will appeal to the widest possible audience.
"These are challenging and exciting times for the Channel as S4C needs to reach consumers on various digital platforms. I believe this team, by working closely with the creative sector in Wales and beyond, can meet the challenge by commissioning innovative and imaginative content."