With this guide you should gain guidance on how to obtain all
Achivements. One concept that makes the whole game a lot
easier is the "undo" button. Hitting this button does not
invalidate achievements and with patience will guarantee a
successful roll no matter how unlikely the original odds.

Aside from this questionably ethical step the general strategy of
the game seems to be to position marines with ranged weapons on
overwatch pointing down long hallways toward enemy spawn points.

There is an optional objective in each mission in the "Sin of
Damnation" campaign. That first section of achievements is 14 in
total. The remaining are of a farming nature and count another 14.

Victory is nothing more than survival
Survive "Suicide Mission" without any casualties

Exterminator
Kill 10 genestealers during one turn in the "Exterminate" mission

Watch the claws
Pass the C.A.T. between at least three terminators during
"Rescue" mission

The purging flame
Cleanse both rooms in the same turn during "Cleanse And Burn"
mission
Cleanse with the flamer in one room and two shots of the
assault cannon in the other. Animation of the latter is
unimpressive, have faith.

Our duty is done
Escape with eight or more marines during "Decoy" mission

Unbowed and Unbroken
Wake all unconscious Marines and take no casualties during
"Alarm Call" mission
Restart the level repeatedly until you get the seargeant in
one of the first rooms and a flamer where you want him.

Relic Bearer
The marine that picks up the chalice in "The Artefact" mission
must be the one exiting the map with it

Honour is my shield
Calistarius must survive "Escape Route" mission

Stand together or fall alone
Exit the map with at least 7 marines in the "Regroup" mission,
but not before all have been put into play
Groups should deploy quite often as the turns roll on.

Stand against the tide
Let no terminators die during "Defend" mission

Sever the head and the beast will die
Kill the broodlord in "Unknown Lifeforms" mission
You should see one just shoot it from a distance it dies like a
normal one.

Light in the darkness
Escape with at least two Terminators before the end of the tenth
turn in "Pitfall" mission
Head for the upper level exit full speed and use Force Barrier.

For the emperor and Sanguinius!
Finish the "The Sin of Damnation" campaign

Forged in battle
Get all campaign achievements
After completing all of the above.

The Emperors Finest
Customize your banner
Banner customizer is in the Librarium from the main menu.

Exemplar of the Codex Astartes
Complete a mission without using a single Command Point
You can do this on the first campaign mission "suicide mission"
Don't go on overwatch which might use CP to unjam.

Honour Your Wargear
Unjam a bolter 40 times
Should come naturally.

The Emperor protects
Survive 15 close combat encounters
Should come naturally.

Storm of Iron
Kill 30 genestealers with the assault cannon
Use this space marine despite limited ammo.
Don't go on overwatch which wastes ammo on misses.

Sword of Retribution
Kill 20 Genestealers with the power sword
Aim to send the seargant into close combat a lot.

Breacher
Destroy 20 doors with a Chainfist
Restart the "regroup" mission repeatedly, a chainfist cuts a
door immediately.

Grant us the strength to prevail
Win close assault against Broodlord
On "unknownn lifeforms" mission go into close combat and abuse
"undo" to get through tough odds.

Slayer of Monsters
Kill 5 Broodlords
Get your kill in the "unknownn lifeforms" mission then undo and
repeat 4 more times.

Power of the warp
Kill 6 genestealers with one psychic storm
In the "alarm call" mission navigate at least 6 enemies into a
5x5 area then spam "undo". Also this seems to be bugged so
get Pyroclast then this will pop.

Pyroclast
Kill 6 genestealers in one shot with the flamer
In the "alarm call" mission make sure the flamer spawns nearby.
Navigate at least 6 enemies into position around a corner with
Force Barrier then flame them and "undo" as needed.

Red Thirst
Have a terminator kill 3 genestealers in melee during one turn
Line up three enemies then abuse the "undo" button and spend CP.

Angel of Death
Kill 1000 enemies
Will happen eventually just keep playing.

There is only war!
Kill 40 000 enemies
Hope you like grinding!