Exhibit 99.1 Koppers Holdings Inc. 436 Seventh Avenue Pittsburgh, PA 15219-1800 Tel 412 227 2001 www.koppers.com News Release FOR IMMEDIATE RELEASE For Information: Quynh McGuire, Vice President, Investor Relations 412 227 2049 McGuireQT@koppers.com Koppers Reports Fourth Quarter and Full-Year 2023 Results; Provides 2024 Outlook Record Fourth-Quarter Sales of $513.2 Million vs.$482.6 Million in Prior Year Quarter Record Year Sales of $2.15 Billion vs.$1.98 Billion in Prior Year Record Operating Profit of ...