Aleksander Montwiłł studied at the Jagiellonian University in Cracow.
After his studies he was secretary of the College of Nobles at the starosty of Wiłkomierz ( now Ukmergė), marshal of the nobility in Wiłkomierz and administrator of the estates of Wierszkajnie and Antokol ( Antakalnis) in the Wiłkomierz district.
He was active in charity and supported his brothers.
Alexander was married to the noblewoman Wanda Brochodska h. Prawdzic, with whom he had 5 children:
- Daughters:
- Maria Jadwiga
- Aleksandra Maria
- Alina Sofia
- Sons:
Alexander died in 1908 and was buried in the cemetery at the church in Pobojsk ( Pabaiskas).