The Ireland international has been out for over two weeks since suffering a broken hand in the win over Queensland Reds earlier this month.
However, Gatland confirmed that Bowe, who featured in all three matches in the tour of South Africa in 2009, could be handed a start for the second Test against the Wallabies at the weekend.
"Tommy Bowe is fit and available, he trained today and did contact," Gatland told the official Lions site.
"Tommy is one of the best players that we have got available to us and one of the reasons we took the risk on George North. If Tommy hadn't been fit and available for this week, we probably wouldn't have put George North in at the weekend because the medical staff were saying there was a reasonable chance that his hamstring wouldn't last for 80 minutes.
"They have done a magnificent job because we found ourselves in the situation where we could take the risk on George knowing that Tommy would be fit for the second Test. If Tommy wasn't fit, we probably wouldn't have started George."
The Lions currently lead the series 1-0.