The 32-year-old ex-Celtic and Brighton winger joined the Hatters on a two-year deal last summer and played 26 times.
"Paddy has had to face up to some personal problems in recent weeks," said boss Nathan Jones.
"At the end of the season he came to me and it was soon clear that he wanted to return to Northern Ireland to be closer to his family and to play there again."
Jones added: "It wasn't a straightforward decision for me - Paddy has done well for us, but in the end we reached an agreement and he goes with my blessing."

Moorways was closed to the public in 2016 but continued to be used by swimming clubs until the end of January.
The decision was made in a bid to save about £350,000 a year.
Council leader Ranjit Banwait said that whatever the cost of a new pool, it was important to get it right.
Moorways, built more than 40 years ago, has struggled with maintenance and health and safety issues.
Derby's other big pool, at the Queen's Leisure Centre, is currently closed due to structural problems, although two other pools remain open for public use at the centre.
The Moorways closure was opposed by high-profile swimmers Ross Davenport, who won two gold medals at the Commonwealth Games in 2006, and Olympic champion Adam Peaty, who now trains outside the city.
Mr Banwait said: "To start work on the pool we've set £20m aside as an initial amount of money.
"Potentially the work is going to cost more than that, we are currently looking at the designs... if it means it is going to cost more we will put that money in place.
"The most important thing is that we get this right, this pool's going to be built and it's going to be there for generations to come."
The new 50m pool is expected to be built by 2020.

A Ray Winstone-like voice is programmed to say "Don't even think about it" and "Put it down, put it back" as soon as the card is removed from the bag.
Rebecca Smith, Leanne Fischler and Kirsty Sneddon created the bag for a degree project.
The fourth-year students said the design was "very conceptual".
All three are in their final year at Duncan of Jordanstone College of Art and Design in Dundee.
The bag - designed to be a "unisex satchel" - has all the electronics hidden inside a false bottom.
A slot has been sewn in for a credit card which conceals an led light and a sensor which acts as a trigger to play the voice recordings.
Ms Fischler, 21, said: "As soon as you take the credit card out, it sends a signal and inside the bag we have a whole load of electronics which we coded ourselves using a platform called Arduino.
"It receives a signal when you take the credit card out and it tells the circuit board that the credit card's moved and it starts to play sequences from our recordings."
The students said at first the bag tried to deter you from spending money, saying things like "Don't you think that's a bit much?" and "Oh, not again". After a while the bag assumes you have made the purchase and starts to "publicly embarrass you".
However, if you put the credit card back right away it rewards you with a gruff: "I knew you could 'ear me".
Ms Smith, 21, told BBC Scotland they had been asked to make a project with an "element of whispering".
She said they had designed the bag as a concept, rather than hoping it would be manufactured for the mass-market.
"We're all passionate about using design to create change and starting conversations," she said.
"We want people to see it and interact with it."
Paddy McCourt has left League Two side Luton Town by mutual consent to return to his native Northern Ireland.
[NEXT_CONCEPT]
A replacement for one of Derby's council-run swimming pools could cost more than the £20m the local authority estimated.
[NEXT_CONCEPT]
Three students in Dundee have designed a handbag which berates you for spending money when you try to use your credit card.