The British film star landed in the capital Freetown on Wednesday for his first visit to the country.
Elba told the BBC's Umaru Fofana that citizenship was "the biggest honour I could get from my country".
"I'm no stranger to Africa: I've been in Africa, I've made films in Africa, I've championed Africa," he said. "But Sierra Leone, it's a very different feeling because it's my parent's home."
"The welcome has been incredible, and I've plugged straight into that energy that I think Sierra Leone is rising with.
"The son of the soil is coming back to fertilise the soil."
'Disney in Africa'
As part of that commitment, the Avengers actor said that he wanted to invest in developing tourism, but also spoke about boosting the entertainment industry.
"America or England cannot house my ambition. Africa can house my ambition, I can create another Disney here [and] I can't do that in America."
Elba was born in London in September 1972. His late father grew up in Sierra Leone, and his mother is from Ghana.
The star, who was named People magazine's "sexiest man alive" in 2018, is best known for his work in Marvel films, including the Avengers, as well as for the lead role in Mandela: Long Walk to Freedom.
He also starred in a Netflix movie about child soldiers, Beasts of No Nation, which was filmed in Ghana.
Sierra Leone was hit hard by a civil war between 1991 and 2002, and between 2014 and 2016 nearly 4,000 people died in an Ebola outbreak which also damaged the economy.
'Bright Sierra Leoneans'
Elba said he wanted to help rejuvenate and "rebrand" the country.
He believes that a Sierra Leonean entertainment industry has the potential to tell its own stories to the rest of the world.
"There are a lot of bright kids here who are techno-heads, [they're] really really smart. I feel like I could contribute to building a workforce that supports other nations in film and that's part of my journey."
The passport, Elba told the BBC, would allow him to "come back home as a son of the soil".