Mahara was elected unopposed as he was the only candidate to file nomination for the post.
The official announcement of the election will be made tomorrow at a meeting of the House of Representatives.
Mahara's candidacy was supported by CPN-UML lawmaker Subash Chandra Nembang and seconded by CPN (MC) leader Dev Gurung.
The main Opposition Nepali Congress did not field any candidate on behalf of the party to compete with Mahara.
The NC said it decided not to file the candidacy as it strongly believed that the Speaker of the House of Representatives should be elected unanimously.