Angela's Ashes by Frank McCourt (1996) — the Pulitzer-winning memoir of growing up Catholic and poor in 1930s and 1940s Limerick. The book has the rain, the lanes, the rosaries, and the drink; it also has McCourt's wit. The city's relationship with the book has warmed over time, and reading it before walking the south-eastern lanes adds an extra dimension to a visit.
'Tis by Frank McCourt (1999) — the sequel, set largely in New York after the family emigrated, but still rooted in the Limerick the narrator left. Useful if you want the full arc.
The Country Girls by Edna O'Brien (1960) — not set in Limerick, but the great novel of Catholic rural Ireland in the 1950s; the small-town Munster world that drove characters like the McCourts to the city makes more sense after reading it.
Spill Simmer Falter Wither by Sara Baume (2015) — set on the wild south-west coast of Ireland rather than Limerick itself, but written by a contemporary Irish novelist whose work captures the Atlantic west in spare, vivid prose; an antidote to the heritage-Ireland version of Munster.
The Crooked Cross by Michael Curtin (1988) — a comic novel set in 1980s Limerick that captures the city in the years between the McCourt era and the contemporary revival. Wry, character-driven, and easy to find in local bookshops.