The tribunal also had "considerable concern" that Sullivan was going into his former firm's offices once day a week and that he continued to have contact with some former clients as a trustee or executor.
"Mr Sullivan must realise and understand that he has been convicted of a criminal offence under the Crimes Act and, as a result of the tribunal's decision, cannot continue to practice as if nothing has changed," Kendall said.
Sullivan, in his mid-70s, earlier admitted two charges before the tribunal - one concerning negligence or incompetence concerning a family trust and two estates and the other over his South Canterbury Finance convictions.
Both reflected on his fitness to practise law.
Watch: South Canterbury Finance - One Guilty, Two Cleared
The tribunal, when deciding on an appropriate penalty, said Sullivan had abrogated his duties concerning the family trust to co-trustee Alan Hubbard, the late founder and chairman of South Canterbury Finance.
Sullivan had played no part in the decision to invest more than $600,000 of trust assets in Aorangi Securities, another Hubbard vehicle in a now-collapsed financial empire.
The tribunal noted Sullivan had been censured by it previously.
In 2009 he was found to have deliberately authorised the taking of fees contrary to specific client directions and in 2013 was found guilty of failing to comply with rules of signing authorities for investing funds.
This disciplinary record was taken into account by the tribunal, which suspended him for three years, censured him, and ordered him to pay the Law Society more than $35,000 in costs.
"You have practised as a lawyer for over 40 years. In that time you have built for yourself a reputation and clientele to be envied. Your failures now and your wrong placement of trust in the late Mr Hubbard had the effect of seriously undermining the confidence of the public in the profession," Kendall said.
