Sullivan resigned his ambassador's post for an unsuccessful bid as a Conservative candidate in the May 2011 election, and then weeks later took an executive position with St. John's-based Ocean Choice International, which is controlled by two of his brothers.
In a decision released Wednesday, ethics commissioner Mary Dawson found that Sullivan violated the Conflict of Interest Act by meeting with Department of Fisheries and Oceans officials in his new role as OCI's vice-president of resource management.
However, Dawson determined that Sullivan could not be disciplined because the one-year "cooling-off" period had already expired.
Liberal MP Scott Andrews, who represents Avalon riding in the House of Commons, said the issue is not over, and that he will now ask Karen Shepherd, the commissioner of lobbying, to investigate.
"These rules are in place for good reason. You're not supposed to have access like other Canadians do not have, and he used his access inappropriately," Andrews said.
Andrews said Sullivan is not a registered lobbyist.
"The lobbying commissioner does have the power to [impose] fines, so we'll see where this goes next," he said.
Sullivan, who had been a provincial finance minister under former premier Danny Williams, was hired by OCI in June 2011.
Sullivan is travelling this week and has not been available to comment.
Jim Bennett, a Liberal MHA in Newfoundland and Labrador's legislature, had filed the complaint with Dawson's office.
"I'm pleased that the ethics commissioner investigated it properly and she found that he was in a conflict of interest," Bennett said.
OCI said it stands by its decision to hire him, but will continue to seek input from the ethics commissioner in its business decisions.