A storied but rapidly-shrinking intellectual-property-law boutique, Kenyon & Kenyon LLP, is moving its practice to full-service Texas law firm Andrews Kurth LLP, marking the latest closure from a shrinking national roster of intellectual-property-law firms.

The deal, to be finalized in the coming days, comes after months of defections from New York-based Kenyon, which counts companies including Mattel Inc., Sony Corp. and Volkswagen AG as clients. The firm employed more than 200 lawyers a decade ago but is down to 55 today...