During an appearance in the Royal Court on Friday morning, Coleman admitted all 19 charges, comprising 15 counts of fraud, two counts of forgery and two counts of uttering forged documents.
The 61-year-old committed the offences between February 2007 and January 2017.
He will be sentenced in February.
In a statement, the States police said: 'Stephen John Coleman has today pleaded guilty to all 19 charges levelled against him in relation to fraudulent receipt of money from the JSPCA.
'Throughout the ten-year period he was chief officer of the JSPCA, he took £300,000 of the charity’s income for his own benefit.
'The guilty pleas entered today follow a complex 18-month investigation by Jersey’s Joint Financial Crime Unit. Faced with the evidence we had painstakingly secured, it is clear that he felt no option but to admit to his crimes in full.
'The crimes he committed had a devastating impact on the charity he claimed to serve. He abused a position of significant trust and endangered the vital relationship between the JSPCA and the public.
'Throughout the investigation, the JSPCA has assisted the JFCU in understanding Coleman’s activities, allowing the team to construct the compelling case which has led to today’s result.'