Completed Series

The Grisha trilogy / Leigh Bardugo

The Darkest Minds trilogy / Alexandra Bracken

Red Rising trilogy / Pierce Brown 

Codex Alera series / Jim Butcher 

Mediator series / Meg Cabot

Missing series / Meg Cabot

Airhead trilogy / Meg Cabot

The Black Magician trilogy / Trudi Canavan 

The Age of Five trilogy / Trudi Canavan

The Traitor Spy trilogy / Trudi Canavan 

The Mortal Instruments series / Cassandra Clare

Seven Realms series / Cinda Williams Chima 

Hunger Games trilogy / Suzanne Collins

Pellinor series / Alison Croggon 

Ingo series / Helen Dunmore

Inkheart trilogy / Cornelia Funke

Eon duology / Alison Goodman

The Farseer trilogy / Robin Hobb 

The Liveship Traders trilogy / Robin Hobb

The Powder Mage trilogy / Brian McClellan 

The Twilight Saga / Stephanie Meyer

Old Kingdoms trilogy / Garth Nix 

Keys to the Kingdom series / Garth Nix 

The Seventh Tower series / Garth Nix

The Inheritance Cycle / Christopher Paolini 

Chronicles of Ancient Darkness / Michelle Paver

The Remnant Chronicles / Mary E. Pearson

His Dark Materials trilogy / Philip Pullman 

Percy Jackson series / Rick Riordon

Harry Potter series / J K Rowling

Mistborn trilogy / Brandon Sanderson 

Avry of Kazan trilogy / Maria V Snyder

Study trilogy / Maria V Snyder

Bartimaeus series / Jonathan Stroud

The Riyria Revelations series / Michael J Sullivan

The Riyria Chronicles series / Michael J Sullivan

Reboot duology / Amy Tintera

Southern Reach trilogy / Jeff Vandermeer

Leviathan trilogy / Scott Westerfeld

 

That is 39 series that I have completed as of 27/10/16
If you want a review or my thoughts on any of these series then let me know in the comments and I would be happy to do that.