Darren Say, 46, used the investments to "fund his lifestyle" between 2010 and 2016.
All his clients' money had gone by the time of his arrest, said Essex Police.
Say pleaded not guilty but was convicted at Chelmsford Crown Court of fraud by abuse of position and fraudulent trading.
He was also disqualified from being a company director for eight years.
The court heard Say, from Kestrel Road, Waltham Abbey, invented a pension scheme where he loaned money to investors for their self-invested pensions.
The loans were invested in a property company of which he was also a director.
Det Insp Lee Morton, of the Kent and Essex Serious Crime Directorate, said: "Darren Say used the mechanism of the pension scheme he developed as his personal cash cow, taking money he was responsible for to fund his lifestyle.
"He has let down his clients, who were persuaded that his pension scheme would provide for them in retirement."
He was sentenced to six years for fraud by abuse of position and two years for fraudulent trading, to run concurrently.
Essex Police will now seek to recoup the stolen money under the Proceeds of Crime Act.
A company director who used £1m of his clients' money as "his personal cash cow" instead of investing it in pensions has been jailed for six years.