The actress, who plays Alex Russo in the Disney series, arrived in Ghana earlier today to "witness first-hand the stark conditions of vulnerable children".
"Every day 25,000 children die from preventable causes. I stand with UNICEF in the belief that we can change that number from 25,000 to zero," she said.
A spokesperson for the 17-year-old added to Gossip Cop that she had been "approached more than a year ago" and would be "involved in educating, advocating and fundraising".
Gomez acted as a spokesperson for the organisation's Trick-Or-Treat campaign last year, which encouraged children to help others.