Rankin suffered cramp in his sole Test appearance against Australia in January 2014 then dropped out of favour with the country he switched to in 2012.
"I'm grateful to England for the chance to play Test cricket," said Rankin, 31.
"But with few opportunities in the last two years, I felt it was time to move on at this stage of my career. I'm delighted to be returning for Ireland."
He met with Cricket Ireland last week to seal what is a timely comeback given the imminent World Twenty20 in India.
Rankin's last appearance for England was on 17 January 2014, making him eligible under ICC regulations to play again for Ireland on 18 January 2016.
The Londonderry-born player will therefore be available for the InterContinental Cup match with Papua New Guinea in Australia from 31 January to 3 February and then the ICC World Twenty20 in March.
He made the last of his 82 appearances for Ireland during the 2012 World Twenty20 in Sri Lanka, taking 112 wickets at an average of 24.12 before appearing for England 11 times between 2013 and 2014.
"There's a real opportunity for Ireland to get Test status now, and that prospect was a real lure for me - I'd love to be part of history," he added.

In May, Qatar vowed to improve the rights of migrants in the Gulf state amid growing alarm at their treatment.
But Amnesty said  progress to end exploitation had been minimal.
Among others, the report highlighted that Qatar was "lagging behind" in reforming controversial laws that tie migrants to a single employer.
Amnesty said that requirements that workers obtain exit permits from their employers in order to leave the country were also still in place.
Sherif Elsayed-Ali, Head of Refugee and Migrants' Rights at AI, said: "Time is running out fast. It has been four years since Qatar won the bid to host the World Cup, putting itself in the global spotlight, so far its response to migrant labour abuses has not been much more than promises of action and draft laws."
"Urgent action is needed to ensure we do not end up with a World Cup tournament that is built on forced labour and exploitation."
The Gulf state has seen an influx of foreign workers ahead of the football tournament and expatriates now make up the bulk of the workforce in the country.
Earlier in November, Qatar's Sports Minister Salah bin Ghanem bin Nasser al-Ali told The Associated Press news agency that the country planned to implement labour reforms in the "next few months".
Amnesty says the proposals do not go far enough.
The report said that Qatari officials increasingly acknowledge the need for improvement but that widespread changes must happen in the coming months.
A failure to put serious changes in place would "call into question whether the Qatari authorities are serious about reform," said AI.
More than 180 migrant workers died in Qatar last year and a significant number are believed to have suffered injuries as a result of unsafe working practices.
Qatar is reported to be spending more than $200bn (Â£121bn) on a series of infrastructure projects, and says the World Cup is a catalyst for a nationwide building project.

The injured pets needed amputations following air rifle attacks in Cranleigh, Guildford and Woking in March and April.
Police said Franky Mills, of Long Gore in Farncombe, faces eight charges of criminal damage and eight of a firearms offence.
A five-year-old cat called Ruby was shot in the spine and put down by vets.
Another cat in Cranleigh survived but lost her eye.
Police said Mr Mills had been released on bail and is due to appear before Guildford magistrates on 9 August.
Warwickshire bowler Boyd Rankin will play for Ireland in the World Twenty20 after switching back from England.
[NEXT_CONCEPT]
Qatar is failing to tackle the abuse of migrant workers, Amnesty International has warned, six months after work began on the Fifa World Cup 2022 stadiums.
[NEXT_CONCEPT]
A 19-year-old man has been charged after a cat was killed and others were badly injured in shootings in Surrey.