The jury returned their verdicts to the Nuku'alofa Supreme Court at 10.20am this morning, the Matangi Tonga website reported.
The jury retired on Wednesday afternoon.
The four found guilty were John Jonesse, the New Zealander who was managing director of the Shipping Corporation of Polynesia (SCP), Ashika captain Viliami Makahokovalu Tuputupu, first mate Semisi Pomale and a former director of the Ministry of Transport, Viliami Tu'ipulotu.
The corporation was also charged, and collectively the defendants faced 30 counts, including one charge each of manslaughter by negligence in relation to the death of Vaefetu'u Mahe, 22, the only Tongan whose body was recovered after the sinking.
The only other body recovered was that of Daniel McMillan, a Briton who had been living in New Zealand.
The other 72 passengers and crew who died - including all of the women and children on board - included a New Zealand citizen, and Niuean policewoman Sisiliah Rachelmana Puleheloto, 24.
The Supreme Court trial began on February 11.
The four men have been remanded in custody for sentencing on April 4.
In Tonga manslaughter by negligence can attract penalties of imprisonment not exceeding 10 years.
