Can the Stepfather be the Wali (legal guardian) in his stepdaughter's marriage?

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger. 

The stepfather (husband of the mother) is not a Wali in marrying off his step-daughter, but it is permissible that he be a representative of her Wali in marrying her off.

The Wali of a woman in marriage is: her father, then her grandfather, then her son, then her full-brother, then her half-brother from her father’s side, then their sons or grandsons, then her paternal uncles, then her paternal cousins. Please refer to fatwa 83338.

Allah knows best.