Frankish religion before the conversion is thinly attested and hostile in transmission. Gregory of Tours, writing in the later sixth century, is the principal witness, and he is a bishop describing what he wants replaced, so his notices of idols, of sacred trees and of the beast in the Frankish origin story are notices of what was being suppressed rather than descriptions from within.
The event the whole tradition turns on is the baptism of Clovis at Reims, placed by Gregory after a battlefield vow. Its significance is less the personal conversion than the confession chosen. The other Germanic kingdoms of the west, Visigothic, Ostrogothic, Burgundian and Vandal, had accepted Christianity in its Arian form and so stood apart from their Roman provincial subjects and from the bishops of those subjects. Clovis took the Catholic side, and the Frankish kings therefore acquired the Gallo-Roman episcopate as an instrument of government rather than as a rival to it.
What followed was a religion of saints and relics organised around cities. Martin of Tours became the kingdom's patron, and his cloak, the cappa, gave the words chapel and chaplain to Europe. Royal power was displayed by founding monasteries, endowing shrines and holding relics; oaths were sworn on them, and Gregory's miracle collections show how completely the saint had taken over the position of the older local power at the spring or the tomb.