The 20-year-old striker, who signed for a fee in the region of £3million, has penned a three-and-a-half-year deal at the Reebok Stadium to become the Trotters' third and final signing of the transfer window.
England Under-21 international Sordell has scored 10 goals for Watford this season and Bolton boss Owen Coyle was pleased to acquire the forward.
"I am delighted to have brought Marvin to our club, as there were a number of other Premier League clubs tracking him," he told bwfc.co.uk.
"We know that he has great potential and I am really looking forward to working with him.
"Overall, we're very pleased with all the players we have been able to bring in, as we have strengthened and added real quality signings to our squad."
Bolton earlier signed Ryo Miyaichi having already brought in Tim Ream.
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