The 'New Girl' actress' engagement news comes just a week after the couple announced that they are expecting their first child together, reported Ace Showbiz.
It will be the second walk down the aisle for Deschanel. She tied the knot with Death Cab for Cutie's lead singer Ben Gibbard in 2009. They eventually divorced in 2012, citing irreconcilable differences.
Deschanel, 34, is due to give birth to her first child in summer. She and Jacob, 42, stepped out together at the Emmy Awards in 2014. They started dating after she split from screenwriter Jamie Linden, whom she dated for two years.