Machine learning models have been used to protect the plant from leaf disease by early detection and classification in the field of agriculture. Farmers' principal source of income is agriculture, and plant leaf disease causes them to lose a lot of crop each year. It is essential to provide food for the whole world by detecting disease at an early stage in the farm for future decision-making. However, there is currently no such kind of system in place to forecast a disease at an early stage. The primary goal of this research is to inform farmers about a novel strategy for preventing leaf disease in plants. Through this research and earlier diagnosis, the losses incurred by farmers might be decreased. In this study, we have suggested a unique custom parallel deep convolutional neural network-based model for the classification of leaf diseases on the farm. This proposed CNN model is trained using the plant village dataset with 10 different categories of leaf disease classes. The patterns of leaf images at particular times are utilized in conjunction with computer vision techniques to detect plant leaf diseases. The tomato plant is taken into consideration for current scientific efforts in disease identification, categorization, and diagnosis. Image resizing, cropping, segmentation using k-means clustering and thresholding, and normalization are five different types of data preprocessing techniques used. The suggested approach may accurately diagnose diseases by automatically extracting features using implicit CNN. During comparisons with the testing of the given data, the output of the proposed model is 99.65%, which is better than transfer learning models available in the literature. This suggested model may be checked for consistency and reliability, and farmers can use it as a practical tool to protect their leaf plants from any kind of disease.