The 10-island archipelago off the west coast of Africa completed entry negotiations in December last year. In May parliament ratified the accession, which is now awaiting approval by the President Pedro Rodrigues Pires.
"We expect the president to sign the protocol this week," the trade official said.
Candidates for membership of the WTO, which umpires the world trading system, have six months to ratify accession once entry negotiations have been completed. Membership takes effect 30 days after that.
Cape Verde will be the 153rd member of the WTO, following Ukraine, which joined last month.
Russia is the biggest country still outside the world body. It is holding negotiations this week, although a row with the former Soviet republic of Georgia over Moscow's support for Georgian breakaway regions threatens to delay those talks.
Other big countries still outside the WTO include Algeria, Iran and Kazakhstan. (Reuters)
