President Hassan Sheikh Mohamud said joining the regional trade bloc was a “beacon of hope” for Somalia.
He said it offered “hope for a future of opportunities and prosperity”.
Somalia has been wracked by conflict since 1991 and many parts of the country are controlled by jihadist group al-Shabab.
Some of its neighbours have sent troops to help fight the Islamist group, which is affiliated with al-Qaeda.
The decision to admit Somalia was made after a meeting of heads of member states in Arusha, Tanzania.
Somalia’s Minister of Information Daud Aweis said joining the bloc would open new doors for progress and partnerships.
Negotiations between the EAC and Somalia began in August hosted by the Kenyan government.
The East African Community is aiming to expand its market size as it hopes to integrate all countries in the Horn of Africa.
Earlier this year, EAC Secretary General Peter Mathuki hinted that Djibouti and Ethiopia would also join the bloc.
The Democratic Republic of Congo joined in March last year.
Currently, the EAC consists of seven countries: Burundi, the DR Congo, Kenya, South Sudan, Tanzania, Rwanda, and Uganda.
Source: bbc.com
