Judge Nevin Dawson convicted Turnbull on the 16 charges and remanded him in custody.
The charges Turnbull admitted carry a maximum penalty of seven years' in jail.
Turnbull, according to the SFO, was involved in a mortgage fraud where false loan applications were submitted to a fund management company to purchase 16 properties in and around the Auckland region, between September 2006 and August 2007.
SFO director Julie Read said this afternoon:
"Mortgage fraud is taken seriously by the SFO. In a housing market which has enough challenges for the honest buyer, further costs to borrowing because of other people's dishonesty is not acceptable. The SFO welcomes the guilty plea today."
Turnbull's co-accused, bankrupt property developer and former New Zealand representative bridge player Malcolm Mayer, is serving a six-year jail term for what prosecutors described as a $47m mortgage fraud.
Mayer, in his 50s, in 2013 was found guilty of 26 charges in a SFO prosecution - 16 for dishonestly using a document and 10 for using forged documents - after a lengthy trial.
Mayer is not eligible to apply for release on parole until February next year.