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
Choose all the replies in R’lyehian
Refuse to take part in the ritual
Discover all the murals of the disappeared tribe
Piece together Margaret Wyckwood's memoirs
Find 20 hidden items
Save Mitchell
Make the suspects talk by using a heavy hand
Push Irene Sanders to the limit
Never drink
Deliver liquor to the sailors
Invoke Cthulhu!
Successfully carry out the counter ritual
Chat with a vision
Open the sailor's chest in the whaling station
Enter the beast’s den
Kill 5 inhabitants who are being controlled
Kill or spare Bradley
Escape your fallen territory
Save Drake's life during the fight with the creature
Banish the creature for good
Accept the revelations
Lay your hands on Algernon Drake's treasure
Find Sarah Hawkins
Discover all the small blue bottles
Read all the books of unholy knowledge
Be the plaything of an hallucination
Fall into Fuller's trap
Meet Algernon Drake and accept his help
Learn the secret of the Scylla
Heal all the patients
Read the Necronomicon
Find occult items
Banish the Dimensional Shambler
Banish the Dimensional Shambler using only one dagger
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
Reach the level of Expert in a skill
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
Fail a skill test
Accept the Sarah Hawkins case