The actress opened up about the powerful role at a press conference in London, where she said it was an “absolute gift” to bring the monarch to life, and a gig that was “impossible to turn down."
"The more I read the script, the more it unfolded in front of me and it was impossible to turn down," said Jenna. "I would be crazy to turn it down, it's a gift, an absolute gift to try and bring this to life.
"Funnily when I left Doctor Who the first thing I said was, 'I don't want to do another series for a while,'" she added. "And then Daisy Goodwin (the writer) and Damien Timmer (managing director) took me out for lunch and so it changed. It's been such an adventure. I've loved it."
The series begins with an 18-year-old Victoria learning that her uncle has died and she is now the Queen of England. While some may see the royal as an "old bag in a bonnet" – as screenwriter Daisy puts it – the show gives fans an insight into Victoria's earlier years.
"It's been quite a revelation, from beginning to end," said Jenna. "I think she's quite surprising and I'm surprised in how little I knew when I first started. A lot of people instinctively said, 'You can't play Victoria. She's stern and old and wore black for the rest of her life.'
"And actually I don't think people are quite aware of how vivid she is, what a lust for life she has. Considering the way in which she was brought up and the role in which she was born to do, none of that seemed to squash that spirit in her and I find that fascinating.
"She really grows and grows through the series into this formidable woman with a vein of steel yet never loses her humour or her lack of self-consciousness. The wonderful thing about her is that she's so flawed and human and you get to see that."
Writer Daisy, who also attended the press conference at Kensington Palace, added: "I had this notion of this tempestuous teenager suddenly becoming the Queen who really doesn't get on with her mother. From then on, the scenes just sprang from the page and I thought this is the Victoria that people don't know."
Viewers will see Jenna in a new light. The Blackpool-born star, who admitted that she never imagined she would embody "the greatest monarch that ever lived", has never played anyone real before.
Her portrayal of Victoria is accurate to the last detail, from her costumes to her blue contact lenses.
"We started off in dresses that we felt she would have been dressed in by other people – very girlie and young – and I remember I found it hard in scenes where she had to command or deal with the Privy Council. I felt like a little girl, and I realise now it's a great thing," said the actress.
"As we go through the series, we see her business wear, her formal wear; when Prince Albert comes in, we enter a more romantic era with gardenia in her hair. It's been an amazing opportunity for our hair and costume designers to tell a real story," she said.
The pretty brunette went through about 70 pairs of contact lenses, playing around with different camera tests.
"You look at any of the portraits of Victoria and the first thing you see is her eyes, they pop out at you. It's great to look so different," she said. "In terms of comfort, they were fine other than when we shot by candlelight. I was in a rose-tinted world because everything had a haze, which wasn't unpleasant really."
Jenna stars opposite Tom Hughes, who plays Prince Albert, and Rufus Sewell, who portrays Victoria's confidant and close friend, Prime Minister Lord Melbourne.
Apart from acting out the tempestuous relationship between Victoria and Lord Melbourne, who she affectionately calls Lord M, Rufus admitted that his main challenge was the horse riding scenes.
"My horse seemed to think that Melbourne was a bit of a bore and would vocalise it," laughed Rufus. "It was never quite clear which end of the horse the complaints were coming from, but midway through my dialogue would come this noise, which is the sound of an animal complaining about how boring its rider is. I managed to keep a straight face, the same cannot be said of the Queen. My horse was called Rupert so it was very strange to have Rufus on Rupert."
Victoria airs on Sunday 28 August at 9pm on ITV.