BOSTON – Former Treasurer Timothy P. Cahill will pay $100,000 and serve a pre-trial probation period of 18 months to four years after admitting to violating state ethics law, Attorney General Martha Coakley announced.

Cahill had been accused of improperly using $1.5 million of state-lottery money for an ad campaign designed to help his ultimately unsuccessful 2010 gubernatorial campaign. His first trial ended in a mistrial when a jury was unable to reach a verdict.

An agreement between Massachusetts and Cahill was filed in court during a hearing held last week before Suffolk Superior Court Judge Christine M. Roach. In the disposition agreement, Cahill admitted to a civil violation of the ethics laws for his role in running more than $600,000 in lottery ads during the 2010 gubernatorial campaign.

“With today’s resolution, Cahill has now admitted that he violated our state ethics laws during his 2010 gubernatorial campaign,” Coakley said in a statement.

According to the disposition, Cahill’s actions in connection with the timing of the lottery permission ads gave rise to an appearance of impropriety. Cahill agreed that he “knew, or should have known, that he was attempting to use his official position to secure for himself an unwarranted privilege of substantial value.” •