Omar Khayyam was part of the team whose calendar reform underlies the Solar Hijri calendar used for Nowruz.
In the 11th century, the Seljuk ruler Malik-Shah commissioned an astronomical reform in Persia. Omar Khayyam, together with other scholars, worked at an observatory in Isfahan on the resulting Jalali calendar. Its careful solar basis helped establish a highly accurate system for tracking the year and the seasons.
The modern Solar Hijri calendar was adopted much later, in 1925, and it retained the principle of beginning the year near the vernal equinox. Nowruz is the first day of that calendar year.
Khayyam is widely known internationally for his quatrains, but he was also a mathematician and astronomer. The calendar was a collaborative scholarly achievement, not the work of one person alone.