Anthony Banbury said the number of Ebola cases would be brought down to zero by the close of this year, but admitted that the end was "not close".
"We are engaged in an epic battle," he said.
The virus has killed nearly 8,000 people, mostly in Sierra Leone, Liberia and Guinea, where the disease started in December 2013.
Mr Banbury admitted his three month mission had failed to hit its target of 100% safe burials and treatment of 70% of infected people.
But he praised international efforts and insisted "the global response to the Ebola crisis has been extremely successful".
"Going forward it's going to be extremely hard for us to bring it down to zero [cases], but that is what we will do," he told reporters, adding: "I believe we will end Ebola in 2015."
Earlier this week, the World Health Organization said the number of people infected by the virus in Liberia, Sierra Leone and Guinea had passed 20,000.
The WHO said more than a third of the 20,000 cases in West Africa were in Sierra Leone, which has become the worst-hit country.