The 29-year-old was in line for a second four-match ban from the English football governing body for his obscene gesture towards the crowd when scoring the Hornets' opening goal in the 4-1 win.
Deeney reacted to the successfully-converted penalty by sticking his two middle fingers up, which he later put down to frustration due to speculation regarding his future at Vicarage Road.
No further action awaits the striker, though, as the FA does not intend to look into the incident any further.
An FA spokesperson said on Twitter: "Watford's Troy Deeney will not face any formal action following his goal celebration during the game against Chelsea on Monday.
"Video footage was referred to a panel of three former elite match officials, who were asked to consider independently whether it was a red card offence.
"The response was not unanimous, therefore no disciplinary action will follow. Nevertheless, the FA will write to the player and warn him as to his future conduct."
Deeney is therefore free to feature in Watford's trip to West Ham United in the Premier League on Saturday afternoon.