Taxi No. 9 2 11 focuses on Raghav Shastri (Nana Patekar), a cab driver in Mumbai who lies to his wife about his job, pretending to be an insurance salesman. One day, he gives Jai Mittal (John Abraham), the spoilt son of a late businessman, a lift. Jai is fighting for ownership rights of his late father's estate. The cab gets into an accident with Jai escaping as he's in hurry. Jai loses the key to the vault containing his father's will in the back of Raghav's taxi.
Raghav decides to hide it from Jai, who, in search for his lost item, goes to Raghav's house and tells his wife what he really does for a living. She leaves him, taking their son. Raghav decides to take revenge. Raghav and Jai vow to kill each other in their fight for their properties. When Raghav fails to kill Jai he targets Jai's girlfriend, Rupali (Sameera Reddy). As Raghav chases Rupali she is saved by Jai by hair's breadth. Jai lets Rupali escape and he attacks Raghav. They have a dirty car fight but both survive.
Raghav goes to Jai's place. Jai returns to his apartment from a second court hearing regarding his father's estate in defeat, because he doesn't have his father's will. He discovers the will, torn to pieces and pasted on the wall of his apartment. Jai becomes depressed and lonely after his friends leave him. Rupali dumps him, too. Losing everything that used to be precious, Jai realises the hard-hitting life and starts respecting his father and his work.
On the other side Raghav is caught again by police and taken to police station where his wife tells him his real character and problem within himself. Soon, he realises his mistake. Jai, having realised the value of close ones, then bails Raghav out of jail. Raghav insists they have a drink and they go to Jai's house for one. They find out that they share the same birthday. Raghav gives back his will, which he had hidden in the sofa, and says that he had never destroyed it — the torn will on the wall is a fake. Raghav then goes to the railway station to stop his wife and son from leaving him, but arrives a little too late. He goes back home where he sees a birthday cake on the table. He feels that he is hallucinating, but gets a pleasant shock when he sees his wife and son standing there, singing him a birthday song (and finds out that it was Jai who brought them back).
Jai confronts Arjun Bajaj (Shivaji Satam), the friend and custodian of the property of Jai's father, whom he tells that he has realised the value of life. The film ends with Jai rejecting the will and taking back the case, while Arjun Bajaj returns everything and tells him that Jai's father would have been very happy had he lived to that day. They share an emotional hug and Jai leaves.