The 23-year-old midfielder arrives at the Boleyn Ground, from Italian club Sampdoria, where he scored three goals in 34 appearances last term.
A box-to-box midfielder, he was one of the best performing players in Serie A during the 2014/15 campaign, and his signing is a real coup for the Hammers.
He will bring a wealth of talent to the side, as well as over 130 games of experience, despite his young age.
The former Spanish Under-21 international will be looking to establish himself in the Hammers midfield next term, and with Europa League qualification ensured, the East London club will be fighting on four fronts.
Obiang has the potential to be a real star for the Hammers, and signing him is a statement of intent from the club. They intend to impress in Europe, and starting moving towards the upper reaches of the Premier League table.
Following the confirmation of the deal, West Ham fans reacted on Twitter to Obiang’s signing, and it is fair to say that the overall view of the support was that the Hammers had completed a fantastic piece of transfer business.
Pedro Obiang for £6 million can only be good business for West Ham. Industrious, tidy (albeit unspectacular) central midfielder. Top pro too— Tor-Kristian Karlsen (@karlsentk) June 10, 2015
With Alex Song going back to Barcelona West Ham needed a good replacement so signed Pedro Obiang. Cracking business by Bilic.— Charlie Wilkinson (@Charlie59896075) June 10, 2015
Pedro Obiang is also a very good Signing— Andy (@Vantastic_AndyD) June 10, 2015
West Ham will like Pedro Obiang. A complete midfielder who can do a little bit of everything. Good engine and passing ability.— Matteo Bonetti (@TheCalcioGuy) June 10, 2015
Obiang's a great signing, solid midfielder with lots of potential. Shame about Ayew though, good signing for Swansea— Webby C (@AlfieWC) June 10, 2015
#WHUFC have signed a very good midfielder in Pedro Obiang. Industrious and hard working with a lot of potential.— Daniel Padwick (@DanielPadwick) June 10, 2015
Pedro Obiang - solid signing for West Ham! For a central midfield player he is pacey, has good passing ability and ball control...— Connor Hughes (@SAFC_lad) June 10, 2015