Singer Lady Gaga captured two Grammys including best dance recording for Poker Face. (Evan Agostini/Associated Press)

Bestselling pop phenomenon Lady Gaga has responded to a lawsuit from a music producer who claims he's responsible for her successful career and is demanding $30.5 million US.

Songwriter and producer Rob Fusari says the singer, who was his former girlfriend, ditched him as soon as her career began to take off.

The lawyer for Lady Gaga, whose real name is Stefani Germonotta, says the agreement signed between the performer and Fusari was "unlawful."

Court documents indicate the relationship between the pair began as protégé and producer, but then became romantic. Around May 2006, they formed a venture called Team Love Child LLC to promote Germonotta's career. Fusari's share was 20 per cent.

Fusari alleges he was a co-writer on songs such as Paparazzi and Beautiful, Dirty, Rich as well as creating her name and getting her a record deal.

Lady Gaga's lawyer, Charles Ortner, filed a response to Fusari's suit on Friday, saying the arrangement was "structured in such a way as to mask its true purpose — to provide to the defendants unlawful compensation for their services as unlicensed employment agents."

Ortner also says that Fusari and his company violated statutes that bar them from "acting as employment agents without a licence and charging Lady Gaga an unlawful fee for their purported services."

Fusari's lawyer, Robert S. Meloni, called the claim "ludicrous" in a statement to The Associated Press.

Lady Gaga won two Grammys in January: best dance recording, for Poker Face, and best electronic/dance album, for The Fame. She also collected three Brit Awards in February in the U.K., including best international album.

With files from The Associated Press