"Eritrea resumed its activity in IGAD and took its seat" at a summit organised by the seven-nation bloc in Djibouti on Monday, Meskel said on Twitter.
He said the country was ready to work towards "peace, stability and regional integration."
Eritrea suspended its membership of IGAD in 2007 following a string of disagreements, including over the bloc's decision to ask Kenya to oversee the resolution of a border dispute between Ethiopia and Eritrea.
Monday's announcement comes after Eritrean President Isaias Afwerki told reporters during a visit to Kenya in February that his country would rejoin IGAD "with the idea of revitalising this regional organisation."
Isaias, 77, did not attend Monday's summit in Djibouti, sending Foreign Minister Osman Saleh and Presidential Adviser Yemane Ghebreab to the meeting instead.
Workneh Gebeyehu, executive secretary of IGAD, hailed Eritrea's return to the bloc, saying in an official statement: "Let me take this opportunity to welcome back the State of Eritrea to the IGAD family."