Robertson pleaded not guilty to all his charges, which included 28 counts of theft by a person in a special relationship, 11 of obtaining by deception and eight of dishonestly taking or using a document.
It led to a lengthy judge-alone trial before Justice Sarah Katz which began in May.
This morning, in the High Court at Auckland, the judge delivered her verdicts.
She found Robertson guilty of 23 charges of theft by a person in a special relationship, all 11 of the obtaining by deception charges, and four charges of dishonestly using a document.
Robertson was found not guilty of six charges, while the remainder of the charges had earlier been dismissed.
Now in his late 40s, Robertson was convicted of the charges he was found guilty of and remanded in custody until his sentencing in October.
Justice Katz's written reasons for her verdicts were 190 pages long, however, she read a summary of her findings to the court this morning.
The FMA's case was that between 2009 and 2015 Robertson operated various companies including PTT Ltd to assist clients to share and trade on the New Zealand and Australian markets.
He also established a text message alert system for his customers, giving them advice on when to buy and sell assets.
But he also created three schemes to fraudulently extract money from his VIP clients, who were mostly elderly and allowed Robertson to trade shares on their behalf.
In essence, Robertson was running a Ponzi scheme, the FMA said.
Robertson never intended to trade his clients' shares and instead spent most of the money for his own purposes which included funding a lavish lifestyle, the FMA's case outlined.
Expensive European cars, travel by private helicopter, luxury weekend getaways, overseas holidays using private jets and buying expensive jewellery were all bought with the fraudulently obtained funds, the court heard.
Justice Katz said of the theft by a person in a special relationship charges, where Robertson was purportedly trading clients' shares, there were "remarkable similarities" in the evidence of the investors, none of whom had a relationship with each other.
One of Robertson's victims said he was a "very persuasive fella".
"I reckon he could sell ice to an Eskimo," they said.
Another said he was an "extremely skilled salesman".
Justice Katz said Robertson's trading offending was "simply a ruse to extract more money from clients" who were financially naive people who had worked hard all their lives.
The judge said in her summary Robertson had also established a "false paper trail" in an attempt to hide his offending.
When confronted by some of his clients, Robertson would try to evade the issue, promise to send further updates on their investment - which never arrived - or assure them their investments were doing really well, the judge said.
Justice Katz found Robertson guilty of all the shareholding charges and said it was a "deliberate deception" where no share transfers were ever executed.
She found him guilty of four of the eight credit card charges.
Karen Chang, the FMA's head of enforcement, said in a statement today: "We are satisfied with this verdict, as Mr Robertson's actions harmed many New Zealanders."
Asset preservation orders were obtained against Robertson and his company in 2015 after concerns were raised that investor funds may have been at risk.
PTT Ltd and associated entities were placed in liquidation later that year.
