Higgs pair production via gluon fusion, $gg \to HH$, probes the Higgs trilinear self-coupling and is loop-induced already at leading order, which makes it sensitive to new colored states. We study the one-loop effects of the scalar leptoquark $S_{1} \sim(\bar{3},1,1/3)$, including its full yukawa sector and a Higgs portal coupling $\lambda_{S_{1H}}|H|^2|S_1|^2$. We implement the model in FeynRules and use NLOCT to generate a UFO with UV counterterms and $R_2$ terms for MadGraph5_aMC@NLO; it reproduces the Standard Model cross section at $14$TeV to $0.06\%$ and yields a UV-finite renormalized $HHH$ vertex. Independently, we compute the full one-loop amplitude (30 diagramas with tirangle, box and contact topologies) with FeynArts and FeynCalc, reduced to Passarino-Veltman functions;it is UV finite and satisfies the Ward identity for each class of diagrams. Both calculations agree for the partonic cross section between 260GeV and 1TeV. For $M_{S_1}=1$TeV and $\lambda_{S_1H}=1$, the relative effect ranges from about $-15\%$ near threshold to $+2\%$ at $1$TeV, and amounts to $-1.0\%$in the hadronic cross section at $14$TeV. The corrected trilinear vertex alone accounts for less than $10\%$ of the effects, which is driven by $S_1$ loops coupled to the gluons. We discuss the extension to the Manohar-Wise color octet and the $4321$ model at future collider energies.