Jim Clark's plea agreement was filed late Monday afternoon in U.S. District Court in Anchorage.
Clark admitted he conspired with former VECO Corp. executives to hide from state election regulators more than $68,000 in polls and consultants fees for Murkowski's failed re-election bid two years.
Clark's attorney, Bruce E. Gagnon, declined comment. He said Clark will issue a statement Tuesday, when Clark is scheduled to be in court.
Messages left on Clark's cell phone and with Alaska's U.S. Attorney, Nelson Cohen, were not immediately returned.
Efforts to reach Murkowski, a former United States senator and father of current Republican Sen. Lisa Murkowski, also weren't immediately successful.
Two former VECO executives, including CEO Bill Allen, have pleaded guilty to bribing Alaska lawmakers. They have not yet been sentenced, and are cooperating with authorities in the probe that stretches from Juneau to Washington, D.C.
Sen. Ted Stevens is being investigated for a remodeling project at his home in Girdwood, on Anchorage's southern edge. Allen has testified that he sent VECO employees to do extensive work on the house.
Stevens has denied wrongdoing. Beyond saying he's paid every bill presented to him for the remodeling project, Stevens has refused to comment on the investigation.
Rep. Don Young is the subject of a federal investigation that is looking into his campaign finance practices. Young's re-election campaign last year spent $854,053 on legal fees, but he won't disclose how the money was used.
Two former state lawmakers have been convicted of accepting bribes from VECO and are serving sentences in a federal prison in Oregon. Another former lawmaker awaits trial.
Clark's plea extends the reach of the investigation to the governor's office, where Murkowski served for four years.
Murkowski was soundly defeated in the 2006 Republican primary by eventual winner, Gov. Sarah Palin, who campaigned on ethics reform.