The 26-year-old will replace Dries Devenyns, who IAM Cycling was forced to scratch on Wednesday with the Belgian suffering from gastroenteritis.
Howard joined the outgoing IAM team this season after a meagre 2015 campaign with Orica-GreenEdge and has been afforded many notable opportunities including surprise leadership at Milan-San Remo.
The sprinter has returned to basics with IAM, capitalising on his own opportunities and happily piloting other fast-men including the Italian Matteo Pelucchi.
IAM has built a team around Mathias Frank and a general classification bid for the 103rd edition of the Tour but has also outlined stage wins as a priority.
“The sports management at IAM Cycling has attempted to bring together the best team possible for the most important race of the season. Considering our experience, we tried to balance our strengths for three weeks of truth,“ sports director Rik Verbrugghe said earlier this month.
Howard received the call-up on Wednesday and travelled immediately to France ahead of the Grand Depart in Mont-Saint-Michel this weekend.
The former track world champion marked a strong start to the season with IAM winning the Clasica de Almeria and placing second behind solo champion Peter Kennaugh (Sky) at the Cadel Evans Great Ocean Road Race.
Howard raced the opening two weeks of the Giro d’Italia, before the race hit the high mountains, and will enter the Tour on the back of Ster ZLM, which he abandoned during stage five.
He, like the rest of the IAM stable, is looking for a new team for 2017. IAM announced in May that it would fold at the end of the year through want of a co-title sponsor.
“There are obviously a lot more riders on the market and not as many spots available for us so the teams are going to have the power there in the sense they’ve got more options and we’ve got less options,” he told Cycling Central in response last month.