Phytophthora root and stem rot is the most destructive soybean soil-borne disease worldwide and can be managed using soybean cultivars with genes conferring resistance to <i>Phytophthora sojae</i>. Here we show that soybean <i>Rps11</i> is an ~27-kb nucleotide-binding site leucine-rich repeat (NLR) gene that confers broad-spectrum resistance to the pathogen. This giant gene is located in a genomic region containing 12 unusually large NLR genes of a single origin and was formed by rounds of intergenic/intragenic unequal recombination that involves the promoter regions and the LRR regions. Comparison of the genomic region in the Rps11 donor line with its corresponding regions in 29 diverse soybean genomes revealed drastic regional diversification including NLR copy number variation ranging from 5 to 23, and absence of allelic copy of <i>Rps11</i> in all 29 genomes. This study highlights innovative evolution and complexity of an NLR cluster and enables precise selection of <i>Rps11</i> for cultivar improvement.