Long-term trends of wind speed (WS) and significant wave height (SWH) in the Arabian Sea (AS) and Bay of Bengal (BoB) are of great interest to scientists, engineers, climate modelers, and policymakers. It is associated with global climate change and efficient offshore and near-shore socio-economic activity management. In this study, the climatology and variability of mean and extreme SWH and WS are determined during the monsoon (JJA) and post-monsoon (SON) seasons along the Indian coastline during 1979−2021 using ERA5 reanalysis datasets. The ERA5 dataset are validated against altimeter data for SWH climatology during 2016–2020. Furthermore, buoy data of July and November 2021 are utilized for validation of SWH at four locations (Visakhapatnam, Pondicherry, Kollam, and Versova) along the Indian coastline. The non-stationary generalized extreme value (GEV) distribution is utilized to determine the extreme values of SWH and WS. Further, linear trend analysis is also carried out at six key port locations (Paradip, Visakhapatnam, Chennai, Mumbai, Mangalore, and Kochi) along the Indian coastline. The outcome reveals that mean SWH displays an increasing trend (Paradip, Visakhapatnam, Chennai, Mumbai, Mangalore, and Kochi) during the JJA and SON seasons, while mean WS shows a decreasing trend in the JJA season and an increasing trend in the SON season. The maximum rate of increase in extreme SWH is observed at Kochi (r = 0.78 cm yr− 1) and Paradip port (1.32 cm yr− 1) during JJA and SON seasons, respectively. In SON season, extreme WS exhibits an increasing trend at all six locations, and the rate of increase is maximum at Visakhapatnam (3.46 cm s− 1 yr− 1), followed by Paradip (3.39 cm s− 1 yr− 1) and minimum at Mumbai (1.84 cm s− 1 yr− 1). Kochi and Paradip ports experienced a significant increase in extreme SWH and WS during JJA and SON seasons, respectively.