Constantine made her name hosting fashion shows like What Not To Wear alongside Trinny Woodall.
She said: "I am sick with nerves and jangling with excitement, and I'm starting from a very low bar. That's fine because I can only improve."
Venn is known for playing nurse Jacob Masters in the BBC medical drama.
The actor also played Ray Dixon in EastEnders from 2012-13 and was in Dream Team and Footballers' Wives.
He said: "It truly is a pleasure to be a contestant on Strictly Come Dancing, to be associated with a show that has such a huge following excites and scares me in equal measure.
"Dancing on Strictly is going to be quite a challenge but life's all about testing yourself so there's lots to look forward to. Let the games begin!"
Blue singer Lee Ryan is bringing his boy band moves to the dance floor. The pop star and former EastEnders actor said he was "so excited" to be part of the BBC One show.
He follows bandmate Simon Webbe, who was a runner-up on the programme when he took part in 2014.
He said: "They approached me and I saw Simon did it and just watching him and his transformation was really important, he really grew and that's what the show's about."
Joining him will be Lauren Steadman, a double world champion paratriathlete and a silver medallist from the Rio de Janeiro Paralympic Games. She is also six times European champion.
She was born missing her lower right arm and has been competing internationally since she was 13.
She said she probably wouldn't wear a prosthetic because "maybe with a spin it would fly off somewhere".
BBC News presenter Kate Silverton said she was "looking forward to the fun, laughter and all the challenges ahead" when her participation was revealed last week.
"It's something of a departure for a news journalist, shifting focus from the headlines to my hemlines," she said in a statement.
Comedian Seann Walsh, a regular on TV shows Virtually Famous and Play to the Whistle, will join her on the dance floor.
"Having seen videos of me dancing on friends' phones from the night before, it's safe to say I'm petrified but also so excited," he said.
Former Pussycat Dolls singer Ashley Roberts has kept a high profile as a TV star since the group split up in 2010.
She has been a guest presenter on Ant and Dec's Saturday Night Takeaway and a judge on BBC talent show Let It Shine.
She said she was "nervous, excited" and "anxious to learn something new, to put on the costumes and become the characters".
She added: "I'm just going to throw my heart and soul into this."
TV presenter and journalist Stacey Dooley has been making documentaries for the BBC for nearly 10 years and was recently given an MBE.
"Typically, work for me is very serious and can be quite hardcore so I'm going to soak up the escapism and bathe in the sequins," she said. "See you on the dance floor!"
TV medic Dr Ranj Singh is also swapping his scrubs for sparkles on the popular autumn show.
The doctor, who has segments on ITV's Good Morning Britain and Watchdog on BBC One, started his TV career five years ago on the CBeebies show Get Well Soon.
He said: "I'm so overwhelmed and excited to be part of this wonderful show. It's an absolute dream come true for me!
"Anyone that knows me knows that I love a bit of sparkle... so bring on the glitter! I can't wait!"
Cricketer Graeme Swann was announced as the sixth contestant on Wednesday evening.
The ex-England bowler will be hoping to emulate the success of Darren Gough and Mark Ramprakash, Strictly champions in 2005 and 2006 respectively.
The 39-year-old said he was worried about waxing his chest.
"It gives me clammy palms just thinking about it. It is going to be horrific. I've never been taught how to dance, I don't know anything."
More Strictly hopefuls
Vick Hope, who hosts the Capital FM breakfast show with Roman Kemp, became the fifth confirmed participant on Wednesday morning.
"It's a bit of a turn-up for the books to be honest," she told listeners.
"I'm a fan of the show and I feel very honoured to be a part of it. I promise you I'm going to work so, so hardI'm so excited."
The 28-year-old presenter, who was born in Newcastle and studied at Cambridge, also hosts Sky One's Carnage and has been a digital reporter for ITV shows The Voice and The Voice Kids.
"I don't really know what I'm doing to be honest," said the 26-year-old Youtuber Joe Sugg after his identity was revealed on Tuesday.
"I know it will be a huge challenge but that's what life is all about I guess."
Joe's main YouTube channel, featuring pranks, dares and impressions, has more than eight million subscribers.
Faye Tozer, whose involvement was confirmed on Monday, said being on Strictly was "a dream come true" and that she would "relish every moment".
The 42-year-old said her participation represented "everything my nine-year-old self ever wanted from showbiz".
The singer, actress and TV presenter rose to fame in 1997 as one of three female co-lead singers in British pop outfit Steps.
After Steps disbanded in 2001, Tozer began a theatrical career before rejoining Steps for their 2011 reunion.
Red Dwarf actor Danny John-Jules, 57, said he was "absolutely delighted" at the prospect of performing in "glittery spandex".
The British actor is best-known for playing Cat in the cult-sci-fi comedy.
His other recognisable roles include the policeman Dwayne Myers in the long-running BBC crime drama Death In Paradise and Barrington in the BBC comedy Maid Marian And Her Merry Men.
Former model Katie Piper claimed she lacked "natural rhythm" and said it was "a bit daunting" to be taking part in the programme.
The 34-year old also admitted that when she told her husband about it, "he just thought I was joking".
Piper was the victim of an acid attack in 2008 that left her blind in one eye.
She has since presented programmes including Channel 4's Bodyshockers and has set up a charity to help people those with facial disfigurements, burns or scars.
The new series of Strictly will kick off with a launch show on BBC One in September, with the full series returning later on in the autumn.