It means Watford are already on their fourth manager of the season and comes after Billy McKinlay refused the club's request last night to accept a reduced role under the new boss, says the London Evening Standard.
McKinlay - who only succeeded Oscar Garcia last Monday - is expected to confirm his departure from the club today with Watford having announced the new appointment at lunchtime.
The Scot has been replaced by former Chelsea midfielder Jokanovic, who until recently was head coach of Hercules in the Spanish Third Division.
Jokanovic led Serbian side Partizan Belgrade to the double in 2007-08 and 2008-09 before moving on to Muangthong United in Thailand and an underwhelming spell at Levski Sofia.
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