Off contract since the end of last season, the midfielder has been working his way back from a knee injury suffered in February 2024.
Given his progress, Brentford have handed Dasilva, 27, a deal to June with an option for another year. The agreement was announced before Saturday's stunning win against Liverpool.
Brentford manager Keith Andrews said: “I’ve been keen to get this done and had discussions with Phil Giles around it, stressing the importance of Josh to the group.
“He’s someone that I’ve involved a lot around the next chapter of where we’re going with the club and the steps we need to make.
“Josh is someone who really understands Brentford Football Club and he’s a really intelligent young man who cares about the club - I don’t think we should forget that.
“But, ultimately, we want to get him back on the grass because, if we get him back to the level he was at, he’s going to be a major asset for us.”