The 20-year-old has been restricted to just one substitute appearance for the Hammers this season, but has spent loan spells at Leyton Orient and Scunthorpe, and could feature in Saturday's home clash against Coventry.
"I was hoping somebody would come in for me so I've been ready and preparing myself physically and mentally for the opportunity," Spence told BBC Radio Bristol.
"I'm here to play and do well for Bristol City first and foremost, and then the experience and where that takes me will be a positive thing as well.
"I operate at right-back or centre-half. I'd like to say I'm a composed defender, I've been brought up obviously playing football at West Ham, and one of my key attributes is that I'm quite quick and I look to get forward when the time's right."