Barcelona agreed a €40 million (£35m/$47m) deal for the 21-year-old in March, with the move initially agreed for January 2019 following the end of the Brazilian domestic season.
With the exit of Andres Iniesta, it was speculated that Barca might try to force the move through sooner, but Gremio insisted in May that they were not willing to let their star midfielder leave until next year, once their Brasileirao and Copa Libertadores campaigns had finished.
However, despite Gremio's initial desires, Barcelona have been able to agree a deal to bring the Brazil Under-20 international to Camp Nou this month, with Arthur holding a press conference to thank his fans for their support.
“I wanted to go out in a press conference for the love I have for the Gremio fans," Arthur said, as reported by as.
"I am fulfilling a dream and for this I have to thank them. It is not a goodbye, it is a see you later and I hope to be able to return one day.
“Barca asked to arrive this summer and it was the clubs that spoke, I did not participate in the negotiations. Barca are the biggest club in the world. It has been my dream since childhood to play for them.
"People talk me about the club, the city and the fans. I have many expectations with my arrival in Barcelona."
Gremio sporting director Andre Zanotta also confirmed the imminent transfer, introducing the midfielder to the press conference, where he revealed that a deal would be finalised this weekend.
“Arthur will travel to Barcelona this weekend. Today he is here to say goodbye to Gremio,” Zanotta told reporters.
“We are closing the sale of Arthur, some small details are missing that will not be ready until tomorrow.”
During his time at Gremio, Arthur won the Copa do Brasil and the Copa Libertadores and was also named in the Campeonato Brasileiro Serie A team of the year for 2017 as he lifted the individual award for best newcomer.