The former X Factor contestant confirmed the news during an appearance on Ireland's The Saturday Night Show.
Henderson told host Brendan O'Connor: "Today's the first day I can announce I'm signed with Sony.
"I'm just so, so excited to go into a studio and finally do what I've always wanted to do. I have already written stuff, but I can't wait to write new stuff because I haven't written all through the period of being on that show and I've experienced so much and so many emotions that I never felt before so, it's gonna be really exciting."
She said of the period since her exit from The X Factor: "It's been absolute[ly] manic. When I was in the show I felt like I was under a lot of pressure... It's a tough one and I am young, so I did feel the pressure a bit, but coming away from it I've just had so many opportunities now."
The 16-year-old also revealed that she had doubts about her singing before entering the reality show and would wonder when she would get her big break.
"It's amazing what this show has done to me," she said. "If I look back six or nine weeks ago, nobody had a clue who I was... I think at the age of 16 it's something that a lot of girls and boys want and It's something I thought was so out of reach from me.
"I thought there's so many talented people out here, how am I going to get a break? How am I ever gonna do it? It just shows you never know what's round the corner."
Henderson also talked about performing for the Amy Winehouse foundation, describing it as "an honour" and calling the late star "a massive icon of mine".
Watch Ella Henderson perform 'Silent Night' on The Saturday Night Show below: