The pair were arrested outside a nightclub near the Champs Elysees on Saturday and spent a night in jail.
Williams, 35, will appear in court at a later date having accepted a charge of buying cocaine, judicial sources say.
O'Connor, 26, faces a charge of possession. They were found with 2.4 grams of the drug.
Police, quoted by AFP, alleged Williams was seen in a car with two suspected drug dealers. O'Connor was allegedly spotted outside the car acting as a lookout.
Williams plays for the French team Racing 92 and O'Connor is at Toulon.