The prosecutor-turned-television-star decided to leave the programme despite its popularity because it is relocating to Los Angeles from her hometown in Atlanta and she doesn't want to move.
Instead she will stay in Georgia with her husband and children to focus on her self-titled HLN show.
She said: "Leaving such a successful show was a tough decision, but, with the increased requirements of the production's relocation to Los Angeles, it became challenging to balance my most important job - mother to John David and Lucy back home."
Jackie Glass - who sent O.J. Simpson to jail for up to 33 years in a robbery case - is set to replace Nancy in September.
Nancy, 51 has based her television career on being a legal commentator who strongly supports prosecutors.
She formed a tough attitude towards suspected criminals because her fiance was murdered when she was just 19.