Jeremy Kenneth Sage abused his position between September 2008 and September 2010 to dishonestly gain £65,943.13, Cardiff Crown Court heard on Friday.
He also stole £31,000 in September 2005 from Robin Smyth and dishonestly obtained a further £133,508.20, the South Wales Argus reported.
Meanwhile, the 48-year-old also admitted that, between October 1 and 22 2008, he dishonestly obtained a cheque worth £15,874.05 from Norwich Union, claiming he was Robin Smyth.
In addition to this, Sage has also pleaded guilty to counts of theft and perverting the course of justice, relating to an incident on December 20, when he took documents belonging to the Crown Prosecution Service.
Sage will be arrested from prison next Wednesday to answer further fraud and perverting the course of justice charges, relating to an alleged false insurance claim over a watch and an issue regarding the occupation of a rented property.
He will appear at Cardiff Crown Court for sentencing on 30 April after a pre-sentence report has been compiled.