The former Nickelodeon star shared an Instagram pic of herself and Watson, writing "Guesssss what??????" and then showing off the ring, stating, "#Hedidgood."
The singer and actress, 21, has been dating Watson, 30, on and off for three years.
Jamie Lynn was previously set to wed Casey Aldridge, the father of her 4½-year-old daughter Maddie.
Britney Spears’ little sister is getting married, y’all! Jamie Lynn Spears and boyfriend Jamie Watson are engaged.