The singer and entrepreneur was given the role to promote education, tourism and investment for her home country.
The 30-year-old said she “couldn’t be more proud” to be handed the prestigious title.
“Every Barbadian is going to have to play their role in this current effort, and I’m ready and excited to take on the responsibility,” she said.
“I look forward to working with Prime Minister Mottley and her team to re-imagine Barbados.”
As well as her multi-platinum musical talents, Rihanna was hailed for her “significant creative acumen and shrewdness in business” by the Caribbean island’s PM Mia Amor Mottley.
“Rihanna has a deep love for this country and this is reflected in her philanthropy, especially in the areas of health and education,” Ms Mottley said.
“She also shows her patriotism in the way she gives back to this country and continues to treasure the island as her home.”
Already a cultural ambassador for Barbados, her expanded role reflects her “global influence across a much broader range of areas”.
Rihanna, real name Robyn Rihanna Fenty, grew up in Barbados and was propelled to fame after a visiting US producer recognised her talents.
She has scored 14 number-one singles in the US charts, more than any artist except The Beatles, Elvis Presley and Mariah Carey.
Alongside her musical career, Rihanna has amassed an estimated net worth of $210m (£160m), has a number of business ventures, notably in the world of fashion and cosmetics.
The pop star has also been a vocal commentator on political and social issues.
In 2017 she was a prominent critic of President Donald Trump’s response to the devastation wrought by Hurricane Maria on Puerto Rico.
The same year she called for an end to gun violence after a cousin was shot dead in Barbados.
In March she almost single-handedly wiped one billion dollars (£760m) off Snapchat’s value after criticising the app for an advert that appeared to make light of domestic violence.