BOSTON — Voters participating in Boston’s preliminary election will be narrowing the field of mayoral candidates from four down to two.

Democratic Mayor Marty Walsh is seeking re-election to a second four-year term as the city’s chief executive.

His challengers include District 7 city councilor Tito Jackson, who served in the administration of former Democratic Gov. Deval Patrick.

Two lesser-known candidates will also appear on Tuesday’s ballot: Joe Wiley, a health insurance worker making his first run for political office; and Robert Cappucci, a retired police officer and one-time Boston School Committee member.

The top two vote-getters in the nonpartisan preliminary election will advance to the November final.

Walsh emerged from a crowded field of contenders in 2013 to succeed Thomas Menino, the city’s longest serving mayor.