The 13x12x26 metre structure is designed to "provide an express lane to eternal salvation for Ireland’s lapsed Catholics", the bookmaker said.
Pope Francis will arrive in Dublin on Saturday morning and depart for Rome the following evening. The confession box is close to Dublin’s Phoenix Park, where crowds of 500,000 are expected for the pontiff’s visit.
The last Pope to visit Ireland was John Paul II, in 1979.
A spokesman said: "Ireland has changed a lot since the last Pope's visit – gay marriage is legal, we’ve repealed the Eighth Amendment [which prohibited abortion], and even secretly cheered for England in the World Cup.
"With decades worth of sins clocked up since then, we’re providing a convenient means to complete your contrition with your keys still in the ignition. And if the Catholic hierarchy have anything they’d like to get off their chests too, they are more than welcome to take a spin through our mega drive-thru confession box while they’re here."