The largest retailer in the US, Walmart, has announced that it is to offer health insurance benefits to same-sex domestic partners beginning next year.

The second largest employer after the federal government announced in a postcard sent to workers this week, that domestic partners of its US employees will from 1 Jan 2014 be eligible to the health insurance benefits.

Walmart’s change in policy will cover same-sex couples, and the domestic partners of opposite-sex couples who have been living together and in a relationship for a year or more.

Earlier this year, the US Supreme Court ruled to strike down the Defense of Marriage Act, which previously defined marriage as between one man and one woman. The ruling opened up over 1,100 federal benefits to married same-sex couples.

The retailer operates across all 50 US states, and spokesman Randy Hargrove said it was important to the company to develop a single definition for all workers, in the interest of consistency for all.

He said: “Given the diverse world we’re in, we wanted to have a comprehensive benefits packages that appeals to a contemporary workforce,” he said. “We want to attract and retain the best workforce.”

Continuing, Hargrove said it was unclear how many new people will enrol in the benefits program, but that around 1.1 million already did.

Workers will be able to enrol between 12 October and 1 November this year.