Wat Phlab is an ancient forest wat (monastery) that dates back to the Ayutthaya period. It gained significance when King Rama I, Phra Batt Somdet Phutthayotfa Chulalok Maharaj, ordered the construction of a new royal monastery adjacent to Wat Phlab, merging the two institutions into one. This was intended to serve as a residence for Phra Yan Sangworn, a highly respected monk and member of the ecclesiastical council, and it became a center for meditation practice. The royal family was encouraged to study meditation under Phra Yan Sangworn, leading Wat Ratchasitharam to become an important meditation center during that time. Even after Phra Yan Sangworn was later appointed as Somdet Phra Ariyawongsagorn, the Supreme Patriarch, and moved to Wat Mahathat Yuwaratcharam, his students continued the meditation tradition. During the reign of King Rama III, Phra Batt Somdet Phan Nakhon, renovations and additional structures were commissioned at the temple, including a stupa, a vihara, a sermon hall, and a Chinese pavilion. The king had resided at this temple for one rainy season during his ordination, and he officially renamed it Wat Ratchasitharam in 1831. Notably, the stupa was subsequently renovated by King Rama IV, who named it Phra Sirijumphon Stupa.