The midfielder, 30, has agreed to a two-year deal at the Rashid Stadium following a successful season with Sporting Braga, in which he helped the club to a fourth-place finish in the Portuguese Primeira Liga.
He will renew his relationship with Quique Sanchez Flores, the Ahli coach who was employed as his manager during his time at Valencia.
"We're very excited to have him and he'll add significant value to our team," said Ahmed Khalifa, the Ahli chief executive. "He's a good player who's had a fine season in Portugal.
"We needed somebody in this position, someone capable of his performance and playing at his level. He will fit well into the team."
Ahli, runners-up to Al Ain in the 2012/13 Pro League, have one of the youngest squads in the division and the acquisition of a player with Viana's experience could prove crucial.
The Portuguese was present at last week's President's Cup final victory against Al Shabab (see gallery) and therefore has already become familiar with his new teammates. Much is expected from Ahli next season, with the 2009 UAE champions tipped to challenge for the league title, while also defend their recently collected prize and compete in the Asian Champions League for the first time in four years.
"We need his experience next year, as we have many competitions locally and, of course, in Asia, so we required someone of his standing to help the team," Khalifa said. "The value he adds is both technically and in helping our very young team. They need some experienced minds to guide them on the pitch.
"As the President's Cup victory proved, experience, especially towards the end of the season, is vital."
Viana's arrival is sure to expedite the departure of Ricardo Quaresma, the much-travelled winger who joined Ahli during the January transfer window. Turkey's Galatasaray are thought to have expressed their interest, although Khalifa revealed as of yet no agreement has been reached.
"It's not yet decided if Ricardo will stay – that will be a decision taken after discussion with the coach to see his vision for the team," he said. "And the other part is the financial side; if we receive a good offer from another team maybe we can do it."
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