Programmable electrothermal metamaterials offer a unified platform for the tailorable and concurrent control of electric and thermal fields, overcoming the inherent limitations of static multifunctional designs. However, independently manipulating these two intrinsically coupled fields remains a fundamental challenge, especially within systems constrained by fixed material properties or geometry-bound configurations. Here, an electrothermal lattice metamaterial (ETLM) system is proposed that enables concurrent control of electric and thermal field distributions through lattice geometrical patterns. By adopting a modular design strategy, the ETLM enables simultaneous shaping of electric and thermal fields via programmable lattice arrangements. Unlike traditional dual-field metamaterials, the ETLM supports a wide spectrum of field manipulations—including cloaking, concentration, and rotation—across both domains, all governed by a unified topological framework. Furthermore, through numerical simulations, spatial symmetry breaking and dynamically tailorable field states by locally adjusting lattice units and introducing anisotropic motifs are achieved. To validate these capabilities, metal-based 3D printing is leveraged to fabricate various ETLM configurations and experimentally demonstrated robust and simultaneous control of electric and thermal fields. This work establishes a geometry-driven paradigm for adaptive electrothermal control, offering powerful tools for intelligent energy systems, field-responsive electronics, and programmable meta-devices under complex multi-physical conditions.