The former Mamelodi Sundowns and Kaizer Chiefs man has taken over the job from fellow centre-back Bevan Fransman, who has joined PSL returnees Highlands Park.
"I'm very honoured. I was caught by surprise because it is only the first few months for me in the club," said Xulu, who was named PSL Defender of the Season after starring in Maritzburg's best-ever fourth-place finish in the league and maiden Nedbank Cup final appearance last term.
"I think the club has done great things also on its own. I didn't expect such a responsibility but I guess it comes with the experience I have; the leadership qualities that I have.
"I'm really proud of the club with what we achieved last season and I'm looking forward to the new journey which is leading the club to greater things. Hopefully we are going to work together and achieve even more."
He added: "I've dealt with pressure before in my career; I've played for big clubs at a very young age. I think pressure comes with the game and I'll be able to take it."
Xulu gave credit to coach Fadlu Davids for helping him bounce back from a dismal two-year stay with Chiefs following his return to the PSL from Russian side FC Rostov.
"It was my first season for me as far as I'm concerned. I think credit must go to the coach for the belief he had in me as a player.
"And for me and my game, I think I haven't reached my potential ... I know I can do even more. But I was very, very happy with what I did for Maritzburg as a club."
Xulu, who captained Bafana Bafana at the recent COSAFA Cup, will lead United out in the KZN Premier's Cup against Golden Arrows on July 2018 at KwaMashu's Princess Magogo Stadium.