This study explores a novel logarithmic parameterization of the deceleration parameter within the $f(Q, C)$ gravity framework, incorporating a nonlinear functional form $f(Q, C) = \gamma_1 Q^n + \gamma_2 C$, where $Q$ and $C$ denote the nonmetricity scalar and boundary term, respectively, and $n \geq 1$. This approach provides a distinctive perspective on the universe’s accelerated expansion without resorting to exotic fields. Using observational data from Hubble measurements ($OHD$) and the $Pantheon + SH0ES$ Type Ia supernovae dataset, the model parameters were constrained through a $\chi^2$ minimization technique. The analysis reveals a transition from deceleration to acceleration in the universe’s expansion history, with the transition redshifts $z_t \approx 0.98$ ($OHD$) and $z_t \approx 0.76$ ($Pantheon + SH0ES$). The model demonstrates consistency with observations, offering insights into the dynamics of dark energy and alternative gravity theories, while effectively modeling cosmic evolution across epochs.