Romeo is a dog who once lived in luxurious surroundings. One day his owners decide to migrate to London and he is left at the mercy of the servant of the house, who dumps him on the streets of Mumbai. Left to fend for himself, he is soon cornered by the local gang – Guru, Interval, Hero English and a dog-wannabe-cat, Mini, who tell him that this is their domain. Romeo does not know the street lingo and is at a loss for words at first, but he manages to win the gang over with giving them haircuts. They love their new looks and accept Romeo as part of their gang. Together, they set up a successful dog-grooming business until Chhainu, the right-hand of gangster-dog Charlie Anna, arrives to collect "weeklies" (weekly protection money) in the form of bones. Romeo throws Chhainu out, and the others, terrified, go to Charlie to plead their case. Charlie threatens them with his trio of female ninja dogs, whom he calls his Angels, but Romeo tricks Charlie into allowing his friends to leave unhurt.

Romeo then meets Laila, who is singing from a rooftop, they dance and he falls in love. To win her over, Laila tells Romeo he must dance with her in front of everyone at the "Moonlight Club" where she performs. Romeo says yes, unaware that Charlie has long wanted her, and anyone who dares go near her is punished. However, Romeo braves the odds and dances with Laila to win her heart. As Laila starts falling in love with him, Charlie, in a fit of rage, captures and terrorizes Romeo. Romeo then promises that he would make Laila fall in love with Charlie. Romeo does not intend to lose Laila, but plans to deflate Charlie's ego by having a disguised Mini pretend to be Laila and make it clear she's not interested. This only ends up exacerbating Charlie's ire, forcing Romeo to promise him a second meeting with Laila.

The night of the appointment, however, Chhainu catches Romeo kissing Laila, who then shouts at Romeo telling Laila of Romeo's deal with Charlie and she angrily slaps him and says she never wants to see him again despite Romeo's pleas and forgiveness. In a pursuit, Charlie's Angels are wooed by Guru, Interval and Hero English, Chhainu is cornered by a mouse (and smashed with a "jumbo jet") and Charlie is chased and caught by the city dogcatchers. But just before Charlie is caught with a net, Romeo pushes him under the dog-catchers van to escape while Romeo goes, Charlie then convinces Guru, Hero English, Interval and Mini to create a distraction to get the guard away from the van, they all succeed and Charlie jumps on the van and says he will free Romeo using a pin in his chain to pick the lock, but the van begins to drive and he falls off, after which Charlie races after the van, losing the pin in the progress, but thankfully one of Charlie's ear hairs suffice.

They escape but Romeo feels there is no point staying as Laila said she never wanted to see him again, and Charlie badly wants her. The next morning, Romeo throws his sack onto an open train boxcar about to leave the station but Charlie arrives with Laila and the others. Charlie tells Romeo that he is a fool for leaving Laila when she still loves him, that he explained everything to her and says she is Romeo's and no one else's. He lets go of her hand and Laila begins to run after the train, while Romeo holds his hand out for her. Resembling a famous scene from Dilwale Dulhania Le Jayenge, Charlie remarks "where have I seen this before?". She reaches for his hand and grabs it but the handle Romeo was holding had lost its top screws, making him fall off with Laila, after which they raise their heads to each other and say "I love you" in sync. It then goes to the "Moonlight Club" where everyone is back singing a reprise of "Main Hoon Romeo" in party-remix.

• Saif Ali Khan as Romeo, the former pet of a rich family, and a former spoiled brat. When life landed him in a slum, after his initial disappointment, he smoothly talks his way out of trouble. He thinks nothing of lying just to get what he wants; Laila.
• Kareena Kapoor as Laila, a beautiful white female dog and Romeo's love interest. She performs at the Moonlight Nightclub every few nights, where all the male dogs throng every time. There isn't a male dog alive who doesn't dream of dancing with the beautiful Laila someday. She falls in love with Romeo after some events.
• Javed Jaffrey as Charlie Anna, the Don of the slum. Charlie is Big Brother and that is what everyone calls him out of fear. He is dirty, fat and ugly, with a big, bouncy belly. His moods are unpredictable and that is what makes him dangerous, but at in his soul he is just a hopeless romantic.
• Vrajesh Hirjee as Guru, the oldest and wisest among the four goons. The others look up to him for his advice.
• Kiku Sharda as Hero English, one of the four goons, a ruffian and a bit of a slow head just like his friends. He looks mean, but he is actually a harmless chap. He has been born and brought up in the slums.
• Suresh Menon as Interval, the third member of the gang. He is a film buff and a bit foolish.
• Tanaaz Irani as Mini, the last member of the gang of four, the only female, and the only one who is a cat. She is in denial that she is a cat and is a dog-wannabe. She refuses to accept that and thinks of herself as a stray dog, but her friends try to drill some sense into her that she is an alley cat.
• Sanjay Mishra as Chhainu, Charlie Anna's official spy. He reports the goings-on of the slum to Charlie. He is also responsible for reminding all to pay up on their weekly protection money to Charlie on pay-day.

English version

• Michael J. Fox as Romeo
• Cree Summer as Laila
• Ian McShane as Charlie Anna
• Laurence Fishburne as Guru
• Nathan Lane as Hero English
• Martin Short as Interval
• Yeardley Smith as Mini
• Peter Dinklage as Chhainu
• Tom Kenny as The Mouse

Additional Voices

• Keith Anthony
• Greg Berg
• Bob Bergen
• Rodger Bumpass

As a fan of animation, Jugal Hansraj teamed up with Aditya Chopra to write their first cartoon. Nothing came of the collaboration, the writer/director recalls, "till this one day, I was waiting at the traffic signal and saw these dogs playing in the dirt... un-cared for, scruffy looking gang, totally mast in a garbage pile, and I instantly knew the characters of my story." The alliance by producer Yash Chopra and Disney chairman Dick Cook is a first in the field of animation. This also is the first mainstream CGI feature film to come out of India. Visual Computing Labs (VCL), a division of Tata Elxsi Ltd., another computer animation studio, similar to Walt Disney Animation Studios, was involved with everything from visual conceptualisation, character design to animation and final output. Production commenced in January 2007, continuing for two and a half years and involved 150 crew members; twenty-one months were spent on the animation. It also benefited from the use of Tata Elxsi's EKA, one of the world's fastest supercomputers. Though the company did not publicly release the film's budget, Britain's Guardian reported it to be about US$7 million. The first trailer, shown on 12 October 2007 with the release of the film Laaga Chunari Mein Daag, shows the film's crew holding an audition for Romeo; another trailer was later shown with Laila's audition . Though the release was originally scheduled for the summer of 2008, the release was put off to Diwali. The costumes for the lead characters were made at Walt Disney World in Orlando, Florida for the film's Indian promotion. Yash Raj Films worked with Hot Muggs for producing licensed merchandise for the film. Hot Muggs integrated an inaugural concept of incorporating one-liners from the movie like "Tension Not," "Stay Cool" and "I'm Good Na" on coffee mugs. Though many Bollywood actors promoted the film, the two main stars of Romeo, Saif Ali Khan and Kareena Kapoor Khan did not do much promotion. Kapoor told the producers she would be busy promoting her other Diwali release, Golmaal Returns. Khan simply made himself inaccessible.

Yash Raj Films, for the first time ever, held a pre-release screening for film exhibitors on 18 October 2008. It was then released exclusively across local multiplexes on 24 October 2008. During the weekend of its release, the film faced competition from Heroes, hence it opened to a poor response of 40- 45%,^{[clarification needed][18]} which improved two days later to 60–70%.^[19] Its first-week gross of Rs. 45 million (US$912,316)^[20] made it an Indian record for a Disney production.^[21] The film was declared disaster at the Indian box office.^[22] In the United States and Canada, the film debuted in as many as 40 theatres on the same day.^[23][24] On the first weekend, it made US$41,770 (Rs. 2080,000) and placed 49th.^[25] The following week, its gross income came to US$55,202. The film opened with similar results in 23 British theatres, grossing £31,576 (Rs. 2470,000).^[26] The movie fared poorly in Australia with an income of only US$13,233 (Rs. 652,000) from 9 venues;^[27] and in New Zealand it brought in US$604 (Rs. 29,792) from 2 venues.^[28] In Kuwait, the film opened on 23 October 2008 and grossed US$14,549 in the first week.^[1]

Upon its theatrical release, Roadside Romeo received negative reviews from critics. Taran Adarsh gave the film three stars out of five, citing its borrowing from the masala films of 1980s and a predictable story. Another factor he said went against the film was its lack of good music. Though the title track and "Chhoo Le Na" were publicised, they lacked impact. Though the film was targeted at children, he said Charlie Anna's south Indian accent was hard to decipher and comprehend even for adults. Despite the drawbacks, he cited the animation's good quality which could even be compared to international standards.^[29] The New York Times criticised the movie saying, "The animated dogs in Romeo aren’t particularly appealing. They mostly walk on two legs and, unlike Disney characters, don’t wear anything beyond neck gear. They look oddly naked and move awkwardly, which flattens the dance sequences and keeps the film earthbound."^[30]