Ever-present for the Tigers this season, the 23-year-old has been an impressive performer since joining from St Helens at the end of the 2010 campaign.
He will now remain at the Probiz Coliseum until the end of 2014 at least.
Emmitt follows in the footsteps of Jonathan Walker, who recently signed a new contract, and head coach Ian Millward said: "It's fantastic news on the back of Johnny signing last week. We're really excited to have him.
"Jake plays good minutes, is always developing his game and it is a big plus moving forward for the rest of the season."
Emmitt added: "It's great to be here, I'm really happy it's all done and dusted. I'm glad I can now concentrate on moving forward and hopefully having a successful year."
Castleford have been given further good news with Craig Huby poised to make his return from injury in Saturday's Challenge Cup clash with Featherstone.
Rated as the form prop in Super League a year ago, Huby has not played in almost 12 months after breaking his knee cap.
But, in his testimonial year, he is in line to return against Rovers.