Channel NewsAsia reported that the couple had lived in Britain, South Africa and Australia before settling in Singapore in the 1970s.
Jo Essery was 89 years old when she passed away in 2013, while Gerry Essery was 92 when he died in 2015.
They had no children.
In a joint press release, the charities expressed gratitude towards the couple for the posthumous gift.
They said the money would come in useful to fund their various activities.
The money is to be divided equally between three charities – Assisi Hospice, the National Kidney Foundation (NKF) and the Society for the Prevention of Cruelty to Animals (SPCA).
In the 1970s, Jo had volunteered her services for more than four years at the SPCA, nursing sick animals.
She was born in Singapore and lived there until the start of World War 2, when she left for South Africa.
Gerry was born in Britain and came to Singapore in 1931, as his father was working as an engineer there.
When the Japanese invaded Singapore, his father sent him to Australia. A few months later, he travelled to South Africa where he was reunited with his family.
It was also there that he met Jo. They got married in South Africa in 1945, when they were about 18 or 19 years old.
The couple moved to Australia in the 1950s where Gerry worked as an accountant for a chocolate company.
They decided to make Singapore their home after Gerry got a job at a glass production company there.