Sonu Ke Titu Ki Sweety is about romance versus friendship. Sonu (Kartik Aryan) and Titu (Sunny Singh) have been childhood friends. Sonu had lost his mother years back. He lives with Titu as his father is abroad. Titu has a large family comprising his mother (Ayesha Raza Mishra), father (Pawan Chopra), grandmother (Madhumalti Kapoor), grandfather (Alok Nath) and grandmother’s brother, Lalu Kaka (Virendra Saxena). Titu keeps falling in and out of love. His heartbreaks are painful as he is an emotional guy. Sonu is Titu’s emotional anchor.
Soon after Titu’s breakup with Pihu (Ishita Raj), his family gets a marriage proposal for Titu. The entire family, including Sonu who is like a family member, accompany Titu to meet the girl, Sweety (Nushrat Bharucha), and her parents (Deepika Deshpande-Amin and Rajesh Jais). Except for Sonu, everybody approves of the girl.
Quite reluctantly, Sonu gives his approval too but as Sweety interacts with Titu, him (Sonu) and the family, Sonu gets more and more convinced that Sweety is a manipulative gold-digger and is definitely not the right girl for his innocent and dear friend, Titu. He tries every trick in the book to have the marriage called off but fails. He even takes Titu’s grandfather and Lalu Kaka into confidence but there’s nothing that happens in that direction. By now, Sweety becomes aware that Sonu wants Titu to call off the marriage. Headstrong as she is, she challenges Sonu to stall the wedding while admitting that she is not a nice girl.
It is now a virtual tug of war. Sonu desperately tries to make Titu realise his folly while Sweety is sugar-sweet in her interactions with the family so as to win over the family members. Even as the wedding date is approaching, Sonu and Titu take off for Amsterdam for a bachelor’s party and, under grandma’s instructions, are accompanied by grandpa and Lalu Kaka. In Amsterdam, Sonu tries to set up Titu with his ex-love, Pihu, who then accompanies them back to India to attend the marriage of Titu and Sweety. Sonu has, of course, taken Pihu into confidence and she plays along as she loves Titu. On his part, Titu also realises that he still loves Pihu.
What happens thereafter? Does Titu marry Sweety? Or is Sonu successful in breaking the impending marriage of Titu and Sweety? Does Titu marry Pihu? Or does Sweety turn out to be the best girl for Titu?