Tuning the magnetic and electronic properties of the double perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>La</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>CoIr</mml:mi><mml:mrow><mml:mn>1</mm

The ${\mathrm{La}}_{2}{\mathrm{CoIr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{6}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ double perovskite series serves as an effective platform for investigating the evolution of magnetic and electronic properties as a function of chemical pressure (doping) or hydrostatic pressure due to the interplay between the electrons' correlation $(U)$ and spin-orbit coupling (SOC). In this study, the substitution of nonmagnetic ${\mathrm{Ti}}^{4+}$ at the magnetic ${\mathrm{Ir}}^{4+}$ site leads to a systematic decrease in unit-cell volume keeping the monoclinic $P{2}_{1}/n$ symmetry throughout, reflecting the effect of chemical pressure along with a gradual suppression of magnetic interactions. The parent compound $(x=0)$ exhibits a ferromagneticlike state with a Curie temperature ${T}_{\mathrm{C}}=92$ K, which continuously evolves into an antiferromagnetic ground state upon full Ti substitution $(x=1)$ with a N\'eel temperature ${T}_{\mathrm{N}}=14.6$ K. Isothermal magnetization measurements reveal a hysteresis behavior with steplike feature at zero field, indicative of a noncollinear magnetic ordering. Additionally, the enhancement of magnetization under hydrostatic pressure on ${\mathrm{La}}_{2}{\mathrm{CoIrO}}_{6}$ $(x=0)$ suggests the presence of piezomagnetic behavior. Thermal expansion measurements on ${\mathrm{La}}_{2}{\mathrm{CoIrO}}_{6}$ highlight a coupling between spin and lattice degrees of freedom. The pressure dependence of the transition temperature in the zero-pressure limit, calculated using Ehrenfest's relation, shows good agreement with magnetization data under applied pressure. First-principles density functional theory calculations performed for $x=\mathrm{0}, 0.5$, and 1 further reveal that strong SOC associated with Ir plays a decisive role in shaping the electronic band structure, with the insulating gap progressively widening as Ti content increases from 0.28 eV $(x=\mathrm{0})$, 0.44 eV $(x=0.5)$, and 1.01 eV $(x=1)$. The magnetic moment decreased more than 50% for $x=0.5$, showing the decrease in magnetic exchange pathways. Collectively, these results establish ${\mathrm{La}}_{2}{\mathrm{CoIr}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{6}$ as a model system for exploring the interplay among electrons' correlation, SOC, chemical pressure, and doping-driven magnetic phase transitions, providing valuable insights into the tunability of electronic and magnetic properties in complex oxides.