The musicians had denied breaching copyright but lost their case at a court in California this week, following a trial that lasted around a year.
Both Robin and Pharrell had testified.
Marvin Gaye passed away in 1984 and his children own copyright to his works.
Outside the courtroom, the family spoke of their joy at the verdict, saying they felt "free from Pharrell Williams and Robin Thicke's chains and what they tried to keep on us and the lies that were told."
It's believed that 'Blurred Lines' - which topped the charts across the world - generated around £11 million in profits.
Robin and Pharrell issued a statement via lawyers yesterday, saying: "While we respect the judicial process, we are extremely disappointed in the ruling made today, which sets a horrible precedent for music and creativity going forward."
It continued to say that 'Blurred Lines' was "created from the heart and minds... and not taken from anyone or anywhere else. We are reviewing the decision, considering our options and you will hear more from us soon about this matter."
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!