26-year-old Omlin joins the Ligue 1 side for a fee between €5m and €6m and will replace Geronimo Rulli.
— MHSC (@MontpellierHSC) August 12, 2020
Omlin brings plenty of experience, having played in both the Champions League and Europa League for Basel.
He was the starting goalkeeper for the Swiss club, but has been out since the end of July with an injury.
Montpellier had on-loan Gero Rulli in net last season, but he has been returned to parent club Real Sociedad.
With the signing of Omlin, the club have recruited their two priorities: a goalkeeper and attacker (Stephy Mavididi).