The exact nature of Sheldon Silver’s lucrative outside legal work had long been one of the best-kept secrets in New York politics.

For years, Mr. Silver, a Manhattan Democrat, maintained that his law clients were just “plain, ordinary, simple people,” but he offered little else about how he earned often hundreds of thousands of dollars a year while also serving as speaker of the State Assembly.

On Tuesday, during Mr. Silver’s political corruption trial in Federal District Court in Manhattan, that veil was lifted by lawyers from Weitz & Luxenberg, the firm where he worked for more than a decade.

Mr. Silver performed no actual legal work, according to Gary R. Klein, the managing attorney at Weitz & Luxenberg; his income came instead from cases he referred to the firm.