The beta decay of the lightest charmed baryon.+ c provides unique insights into the fundamental mechanism of strong and electro-weak interactions, serving as a testbed for investigating non-perturbative quantum chromodynamics and constraining the Cabibbo-Kobayashi-Maskawa (CKM) matrix parameters. This article presents the first observation of the Cabibbosuppressed decay Lambda(+) (c) -> ne(+)v(e), utilizing 4.5 fb(-1) of electron-positron annihilation data collected with the BESIII detector. A novel Graph Neural Network based technique effectively separates signals from dominant backgrounds, notably Lambda(+) (c) -> Lambda e(+)v(e), achieving a statistical significance exceeding 10s. The absolute branching fraction ismeasured to be (3.57 +/- 0.34(stat.)+/- 0.14(syst).) x 10(-3). For the first time, the CKM matrix element |V-cd| is extracted via a charmed baryon decay as 0:208 +/- 0:011(exp): +/- 0:007(LQCD) +/- 0:001 tau(+)(Lambda) (c). This work highlights a new approach to further understand fundamental interactions in the charmed baryon sector, and showcases the power ofmodernmachine learning techniques in experimental high-energy physics.