The 30-year-old Saracens lock becomes the first Black player to captain the Lions and only the third Englishman in 89 years to be appointed leader of the touring side.
"I will do my best to do the role justice. I am very much looking forward to the challenge ahead, it’s going to be a great tour," he said.
"I know the appetite amongst the players is extremely high, everyone is hungry to be a Lion and I can’t wait to play my role."
One of the few sure test starters, Itoje will be embarking on his third Lions tour after being selected as the youngest player in New Zealand in 2017 and playing a standout role in South Africa in 2021.
Appointed England captain in place of Jamie George in January, Itoje led his country to second place in this year's Six Nations Championship with four wins in a row.
The first Englishman to lead the Lions since Martin Johnson 24 years ago, and only the second in the professional era, the London-born son of Nigerian parents was the obvious choice after Ireland captain Caelan Doris suffered a shoulder injury.
Itoje said he heard the news on Tuesday when he got an unexpected call on his mobile from an Irish number. Lions head coach Andy Farrell is also coach of Ireland.
Even though the signal was poor, and he did not have Farrell's number saved, he recognised the coach's English accent.
"It's a tremendous honour, privilege, you think about the people who have held this position before and it's remarkable," Itoje said.
Itoje had dinner on Wednesday with past captains and said their passion and appreciation shone through.
"It was amazing to be a part of that. It’s our responsibility now to take it forward and to make sure the Lions continues to be in an elevated position," he said.
Itoje showed he was captain material from an early age, leading the England Under-20s to Junior World Cup triumph in 2014, though he became Saracens captain only this season.
"He has thrived on the England captaincy. He played really well in the Six Nations, but he has played even better for us since then," Saracens director of rugby Mark McCall told the Guardian this week.
"Maro has absolutely thrived on all of that leadership," he added. "Maro is very much a leader by what he does and how consistent he is."
The Lions have a game against Argentina in Dublin on June 20th. They will have five tour games before the first test in Brisbane on July 19th. The second and third tests are on July 26th and August 2nd.