Aminatta Forna won Best Book and 10,000 for her novel The Memory Of Love because of its "risktaking, elegance and breadth".
According to the judges, the book is an "immensely powerful portrayal of human resilience" which "delicately delves into the courageous lives of those haunted by the indelible effects of Sierra Leone's past".
Now in its 25th year, the Commonwealth Writers Prize recognises the best fiction from Commonwealth countries. Louis de Bernires, Andrea Levy, Ian McEwan and Zadie Smith are previous winners.
Forna was born in Glasgow but lives in London. She grew up in Sierra Leone, west Africa and has been involved in development projects there.
She said she hoped she had made Sierra Leone proud. "This means very many things to me, but mostly that Sierra Leone has won its first literary prize," she said.
"We have had a struggle in the past ten or 15 years and I just hope I have made them proud".
Her first book, The Devil That Danced On The Water, was shortlisted for the Samuel Johnson Prize in 2003.