The 22-year-old spent over a decade with the Blues, coming through their academy, and his form earned him England youth caps at every level.
However, following a number of spells on loan, a lack of first-team opportunities left the midfielder on the fringes of Antonio Conte's squad and he decided to seek pastures new at Vicarage Road.
Regular football clearly suits him and last week he earned his maiden call-up to the senior England squad after impressing for the Under-21s over the summer.
With him in the running to make his full international debut in the upcoming internationals against Malta and Slovakia, Chalobah believes the decision to join the Hornets is already paying off.
"It takes a lot [to leave a club like Chelsea] and I think you have to really look deep into yourself and see what makes you happy," Chalobah said.
"The problem was that I wanted to play. After getting a taste of it last year, I needed to go out and try and do better things for myself.
"I think you really have to be brave, and sometimes decisions can be hard to make, especially when it is your future, and you have to make those decisions yourself.
"So for me it was a hard decision, not easy. I had to put a lot of things into consideration but now I can say that it was a good decision."