Joseph served as a legislative aide for Gillibrand and also worked on President Obama's 2012 presidential campaign, according to NY1.
Joseph previously served as the political director for Weiner's campaign, according to the New York Daily News.
The previous campaign manager, Danny Kedem, resigned a week earlier amidst news that Weiner had continued having sexually explicit interactions with women on the Internet after the scandal caused his resignation from Congress.
In an interview with NY1, Weiner said he has given a "pretty good summary" of his racy online interactions.
"And I guess the question becomes: Well, what was my obligation? Was it to say all right to say, 'This person and that person and this was the time and this was the date,' and say, 'I'm going to decide I'm going to out everyone who was involved in these conversations with me, whether it was good for them or bad for them or indifferent?'" Weiner said. "And I said I wasn't going to do that. So to some degree, this notion that I haven't been completely transparent, yes, I haven't let people into every last embarrassing thing that I did. But I gave them a pretty good summary."