In chapter 700 of Naruto manga (last chapter) it was shown that Uzumaki Naruto finally reached his dream of becoming Hokage. It was also shown that he didn't achieve it immediately after the 4th Shinobi War ended as Hatake Kakashi was the 6th Hokage and Naruto was the 7th.
AFAIK, even when fighting Otsutsuki Kaguya, Naruto was a Genin as he never passed the Chuunin nor Jounin exam (as far as the manga is concerned). There is an anime where Naruto took the Chuunin exam, but he failed after disqualified due to using Sage Mode.
It was shown in Naruto the Movie "Road to Ninja", that to become Jounin, one must become a Chuunin first. However it is also to be noted that double promotion is also possible.
4th, 5th, and 6th Hokage were all Jounin prior to being Hokage. I'm not sure about the 1st, 2nd, and 3rd Hokage, although strength-wise they are stronger than your average Jounin. The next Hokage was chosen either by the current Hokage, or the Daimyou of the Land of Fire. No other requirements was listed on the Wikia.
So, to the question, has Naruto reached the rank of Jounin when he was selected as the 7th Hokage? Or was he still a Genin, since it didn't actually matter much considering that everyone knows who he is, that he was the hero who saved Konoha from Pain, and more importantly the world from Infinite Tsukuyomi.