As befits his office, the bulk of his known works is for liturgical use: six masses (including a “parody” on the Flemish-Dutch-language-song “Ick seg adieu”, meaning “I say farewell”, and one on the chanson “Si du malheur” by his master Lassus), some antiphonies and litanies. Thus he composed his antiphone “Vidi aquam” a 4 for the sprinkling of holy water, which was substituted in Mass from Easter to Pentecost for “Asperges Me”, in the alternatim-tradition, quoting the Gregorian plainchant melody both as cantus firmus and as paraphrase.
As his name (which can however also be read in Latin as a toponymical reference to something dig, a plausible latinization, e.g. of such Dutch names as Vandegracht) suggests, he is thought to be a native (or descendant of such a family) of Fosses in Namen (= Namur), in the presently Walloon (francophone Belgian) Ardennes (though others call him a German composer) and presumedly trained in nearby Liège, then an independent prince-bishopric. From 1596 he was the Unterkapellmeister (deputy) of the great composer Orlando Lassus (mainly director of the choir) of the Bavarian dukes in their capital München (Munich), and at Lassus’s death succeeded him as Kapellmeister in 1594 untill he was replaced in 1602 — probably gravely sick — by Orlando’s son Ferdinand Lassus; he died in 1603, still in Munich.
He is probably identical with the Jean des Fosses who had been a singer to the Duke of Savoy (then still Italian, now French) in 1557.
This contribution is endebted to musicology professor Ignace Bossuyt (KULeuven)’s book “De Vlaamse Polyfonie” (Leuven, Davidsfonds, 1994) and the HOASM-site linking below.