The attacking midfielder made a deadline-day move to the Baggies but was unavailable for last weekend's 1-1 draw at Fulham as he awaited the required paperwork.
That has now been granted to free the 29-year-old Benin international, who cost an initial B£5.5million, to make his Baggies bow against the club with whom he spent two-and-a-half seasons.
"Stephane Sessegnon has today (Wednesday) been granted a work permit," a West Brom statement read.
"The Baggies' club-record signing is now available to make his debut against his former club Sunderland, at The Hawthorns, on Saturday."
Sessegnon, who signed a three-year deal, is set to bolster West Brom's attacking options following a barren start to the campaign in front of goal.
Defender Gareth McAuley's late header against Fulham on Saturday was their first goal in the Barclays Premier League this term.