Staley, the No. 28 overall selection in the April draft, unseats veteran Kwame Harris. The two have been battling throughout the summer for the job.
Harris, the team's 2003 first-round draft pick, has started each of San Francisco's 32 games the past two seasons at right tackle and has a streak of 37 consecutive starts. Harris started the final five games of the 2004 season at left tackle.
Harris started each of the team's first three exhibition games this summer, with Staley alternating in with the first unit. Staley will make his starting debut Thursday in the 49ers preseason finale at San Diego.
"Starting positions on our team are earned," Nolan said. "Nobody is handed a starting role. Both Joe and Kwame had outstanding camps. It was a very close competition. Joe was more consistent. Joe earned the starting position based on his production on the football field both in practice and in the games."
Staley progressed quickly during the summer and performed well in pass protection, which has always been an area of inconsistency for Harris.
According to STATS, Inc., Harris allowed 8.5 sacks last season with four holding penalties and one false start. The season before, Harris allowed 9.5 sacks and committed 15 penalties, seven of them false starts.
Staley signed a five-year contract with the 49ers late last month. Harris is in the final season of the deal he signed with the team as a rookie in 2003.
Copyright 2007 by The Associated Press.