Sampaoli has the benefit of having arguably the world's best player at his disposal and the former Chile and Sevilla coach said Messi was ready to shine.
The relevant paperwork has now been received, and a statement from the Spanish club confirmed the departure of their ex-Chile boss after just one season. "It's a boost for us to see how excited he is with this new stage (for Argentina)", Sampaoli told reporters.
Argentina now lie fifth in their qualification group and only the top four automatically go through to the finals.
JorgeSampaoli has had success with the Chilean national team, leading them to the 2015 Copa America title.
Sampaoli was finally unveiled as head coach on Thursday, signing a deal through to the 2022 World Cup.
That crisis prompted then-coach Gerardo Martino to quit and be replaced by Edgardo Bauza, who was sacked last month.
The LaLiga club announced last week they had reached an agreement in principle with the Argentinian Football Association but set them a deadline of June 1 to complete all the necessary paperwork.
The first competitive match for the new management will take place in August in a World Cup qualifying game in Uruguay.
"It is a dream that I cherished for ages".
Another change Sampaoli plans involves Javier Mascherano, who has featured in midfield for the national team despite playing as a defender for Barcelona. "There are some very good teams trying to do the same thing as us", added Sampaoli.
"I spoke with Leo and we're both excited", said Sampaoli.