Salvin, who was previously with Rotherham, Leeds Carnegie and Worcester Warriors, joined Exeter in 2021 and was part of the coaching team that helped them to PWR finals in 2022 and 2023.
Wales, who enjoyed a morale-boosting win against the Barbarians at Allianz Stadium last Saturday, will host South Africa and USA at Cardiff Arms Park in September before travelling to Japan in October for two Tests.
Former Gloucester-Hartpury head coach Lynn was appointed Wales boss before the 2025 Six Nations and previously brought in Tyrone Holmes as defence coach.
Former Wales and Ospreys centre Ashley Beck was named interim attack coach for the Six Nations and was part of Lynn’s staff for the Baa-Baas fixture.
Lynn, who has won just one of 15 Tests, has welcomed Salvin’s permanent appointment.
“Steve is a coach I knew well and respected from my time in the PWR, but I was really impressed with his technical expertise and how he relates to players in the women’s game,” Wales’ head coach said.
“He made a real impact in a short time during the recent Six Nations, and I am delighted he will now come on board full-time with Wales.”