The market-leading over-50s life assurance plan specialist will now use Golden Charter to source funeral directors for its plan holders who request a funeral benefit option.
The companies have been working together for four years, but Golden Charter said the contract "significantly boosts Golden Charter's market share and choice for consumers".
Sun Life Direct customers will now have access to a network of nearly 3000 independent funeral directors across the UK, which Golden Charter says will support job creation in the profession. The deal will also take its own share of the UK pre-arranged funeral market, which is growing rapidly, above 50%.
Funeral Planning Authority figures show 67,484 pre-paid funeral plans were sold in the UK in the first half of 2013, putting the market on course for growth of 12% this year on the total sales of 120,731 in 2012. The average price of Golden Charter's pre-paid funeral is £3,100.
Last year, when the Church of Scotland announced an investigation into the rising cost of burials and funerals, Sun Life Direct expressed its interest and said the average cost of a burial in Scotland had risen by 66% since 2004 to £3,506.
Ronnie Wayte, managing director of Golden Charter, said Sun Life's choice "underlines the continuing success of the independent sector despite the market power of corporate providers".
Mr Wayte said Golden Charter sales were up by two thirds in the current financial year.
All of Golden Charter's surpluses are used to support its independent funeral director members.