Jurors deliberated for 19 hours before returning guilty verdicts against DeLay on charges of money laundering and conspiracy to commit money laundering. He faces up to life in prison on the money laundering charge.
There was no immediate comment from DeLay or his lawyers.
Prosecutors said DeLay, who once held the number two job in the House of Representatives and whose heavy-handed style earned him the nickname "the Hammer," used his political action committee to illegally channel $190,000 in corporate donations into 2002 Texas legislative races through a money swap.
DeLay and his lawyers maintained that the former Houston-area congressman did nothing wrong as no corporate funds went to Texas candidates and the money swap was legal.
The verdict came after a three-week trial in which prosecutors presented more than 30 witnesses and volumes of e-mails and other documents. DeLay's legal team presented five witnesses.
Prosecutors said DeLay conspired with John Colyandro and Jim Ellis to use his Texas-based Political Action Committee (PAC) to send $190,000 in corporate money to an arm of the Washington-based Republican National Committee.
The committee then sent the same amount to seven Texas House candidates. Under Texas law, corporate money cannot go directly to political campaigns.
Prosecutors claim the money helped Republicans take control of the Texas House.
That enabled the party's majority to push through a DeLay-engineered congressional redistricting plan that sent more Texas Republicans to Congress in 2004 - and strengthened DeLay's political power.
DeLay's lawyers argued the money swap resulted in the seven candidates getting donations from individuals, which they could legally use in Texas.
They also said DeLay only lent his name to the PAC and had little involvement in it.
DeLay has chosen to have Senior Judge Pat Priest sentence him. He faces five years to life in prison on the money laundering charge and between two and 20 years on the conspiracy charge.
The 2005 criminal charges in Texas, as well as a separate federal investigation of DeLay's ties to disgraced former lobbyist Jack Abramoff, ended his 22-year political career representing suburban Houston. The justice department probe into DeLay's ties to Abramoff ended with no charges filed against DeLay.
Ellis and Colyandro, who face lesser charges, will be tried later.
DeLay has been out of the spotlight since resigning from Congress in 2006.