Here is the full list of all 49 Call of Cthulhu achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Refuse the ritual
Refuse to take part in the ritual
Successfully carry out the counter ritual
Invoke Cthulhu!
Choose all the replies in R’lyehian
Chat with a vision
Discover all the murals of the disappeared tribe
Open the sailor's chest in the whaling station
Enter the beast’s den
Piece together Margaret Wyckwood's memoirs
Save Mitchell
Kill 5 inhabitants who are being controlled
Kill or spare Bradley
Escape your fallen territory
Make the suspects talk by using a heavy hand
Save Drake's life during the fight with the creature
Banish the creature for good
Accept the revelations
Push Irene Sanders to the limit
Never drink
Lay your hands on Algernon Drake's treasure
Find Sarah Hawkins
Discover all the small blue bottles
Read all the books of unholy knowledge
Fall into Fuller's trap
Meet Algernon Drake and accept his help
Find 20 hidden items
Learn the secret of the Scylla
Heal all the patients
Read the Necronomicon
Banish the Dimensional Shambler
Banish the Dimensional Shambler using only one dagger
Find occult items
Accept to read an unholy book
Meet Francis Sanders
Make a deal with a crazed inmate
Inspect 50 items
Take part in the ritual in the caves
Fall into the sacrificial pit
Discover the mansion’s secret passage
Use the globe to open the secret passage
Explore the memories of the Hawkins family
Convince the caretaker to help you
Get driven to the Hawkins Mansion
Be the plaything of an hallucination
Deliver liquor to the sailors
Fail a skill test
Accept the Sarah Hawkins case
Reach the level of Expert in a skill