The announcement came in the finale of the UKIP conference and on the eve of the upcoming Conservative conference.
On stage, Nigel Farage introduced the Conservative MP, who announced he is stepping down and joining UKIP.
He follows in the footsteps of Douglas Carswell, who, less than a month ago, made his intentions clear that he would resign from parliament and stand as a UKIP candidate. This triggered a by-election due to take place on October 9th, the same day as David Cameron's birthday.
Reckless, the MP for Rochester and Strood, will follow Carswell's decision and resign from parliament, also triggering a by-election.
At the last election, Mark Reckless got almost 50% of the vote, but Reckless is known, so probably liked, for his eurosceptic views, so has a chance at securing a UKIP win.
Following Carswell's defection last month, a Survation poll, for the Mail on Sunday, gave UKIP 64% in the constituency. The poll was carried out swiftly after the defection so it is likely a poll will follow Reckless' defection. In a couple of days time we will likely know what chances the man has as a UKIP candidate.
Two MPs defecting in one month will cause a serious headache for Mr. Cameron and the front-bench government team. With Carswell expected to win in less than two weeks time, that momentum could help Reckless also secure a victory. By the end of the year UKIP could have two MPs in the House Of Commons, which would render the Conservative claim - that a vote for UKIP is a vote for Miliband – irrelevant in the minds of voters.
UKIP caused an earthquake earlier this year by winning the European elections and remain at about a constant 13% in the polls. If Carswell and Reckless return to the Commons under the UKIP banner then more defections could follow, and ultimately, in 2015, UKIP could keep momentum going and build on their electoral success.
Whether UKIP gain any seats in 2015 will depend on their electoral strategy. Earlier this week, UKIP's deputy leader, Paul Nutall, spoke on the Daily Politics saying that they would be targeting their resources in a number of seats.
The 2015 election is proving more and more unpredictable by the day as a hung parliament is incredibly likely. The UKIP factor only makes things more difficult to predict. It's too simplistic to say that UKIP will only take votes from the Conservatives as the party has done well in recent by-elections in Labour heartlands. The party are taking votes from across the spectrum.
Whether UKIP can turn votes in local and European elections into 2015 general election seats, will only be determined in May. However, with three upcoming by-elections (two of which caused by Conservative-to-UKIP defections) we could get an idea of future UKIP success.
There are so many questions and speculations going on as a result of Reckless' defection, but one massive one will be bouncing round David Cameron's head as he prepares for conference, looking over at his MPs: 'which one of you is next'?