The money was used to repay other investors and to pay for some business and personal expenses between 2010 and 2012, according to the Serious Fraud Office.
The former financial adviser also made false statements in reports to hide the true picture from investors.
The actual losses to Robinson's investors was $2.3 million.
Robinson was the second authorised financial adviser to ever lose his license when the Financial Markets Authority cancelled it in December 2012.
SFO lawyer Rachael Reed said the actual amount stolen was more than $3 million and called the offending an "extensive, premeditated theft by very much a trusted adviser".
"The victims had 100 per cent trust in Mr Robinson with all of their funds," Reed said.
"Their lives have changed considerably as a result of the theft."
Robinson will be sentenced next month.