Potashnik, the government's star witness in the bribery and extortion trial of former Dallas City Councilman Don Hill said he decided to plead guilty and testify against the others just before the start of the trial because "I was guilty."
Search warrents were executed June 20, 2005, at Hill's City Hall office and Potashnik's company, Southwest Housing.
Potashnik had hired Farrington as a consultant and prosecutors have alleged that her payments from Potashnik were funneled to Hill as bribes.
Defense lawyers said that Farrington was paid for legitimate work and that Hill never received any bribes.
Potashnik spent the entire day on the witness stand.
Potashnik said in court that his wife, Cheryl, has also pleaded guilty, but her plea involves the case of Dallas state Rep. Terri Hodge, who will face a separate trial later.
A defense cross-examination of Brian Potashnik is expected Thursday.
Hill's trial could last several more weeks.