Damadamm is about the life of Sameer (Himesh Reshammiya), a writer who writes scripts for Indian films. He works with his girlfriend, Shikha (Purbi Joshi) at the industry. Shikha is totally over-posseive over Sameer, and suspects him all the time. Due to a speciallity, Sameer can't dump her either. He has no idea how to get rid of Shikha's suspicion, until one day her family invites her over for a relatives' wedding. She leaves for a few weeks, and until then, Sameer gets his total freedom. He drinks; parties and even flirts with random girls. One day, enters a new girl into his office, Sanjana (Sonal Sehgal) and its love at first-sight for both of them. The two are then assigned to work together on a film, but Sameer has to be careful, as Sanjana is his boss' younger sister. Whilst working together, Sameer and Sanjana start to fall in love.
During this, Sameer even starts to ignore Shikha's phone calls. Getting fed up, Shikha arrives back home, when she see's how close Sameer and Sanjana have gotten within 15 days she gets jealous, causing an arugment with Sameer and the two break up. She then starts friendship with Sameer, after his boss arranges for Sameer and Sanjana's wedding. But before the wedding Sameer eventually realizes he truly loved Shikha and can't live without her, so he breaks the marriage with Sanjana. Therefore, his boss sacks him, whereas Sameer replies that he would rather pick his girlfriend Shikha then his work. Sameer manages to convince Shikha to give him another chance.
Later the boss rehires both Sameer & Shikha and even throws them a party.