If you have seen Laurence he looks exactly similar to the Cleric Beast you fought in the Main Bloodborne story and now in the expansion Laurence has the similar moves like the Cleric Beast and a bit extra of Fireworks. This bloodborne: The Old Hunters Guide you can beat Laurence with no pain.
As we mentioned earlier Laurence attacks are similar to those of Cleric Beast and if you remember how you defeated him them this will be a piece of Cake for you, but just be careful of the Fire attacks her perform when he is totally charged. Your main focus and strategy here should be on dodging the attacks and maintain your stamina for more powerful attacks.
Jump on your right and get the cover as you begin with the Battle with the Boss Laurence. he will play his old dirty move by releasing the flames in an arc which is similar to the Cleric Beast. Take cover on any of the side so that it makes hard for him to grab you or perform a roll over whenever he picks up his large arm. If you are grabbed by him then he will toss you on the ground like a small kid which can give you a critical damage.
Another Dirty move by Laurence is by Jumping in the air and land on top of you like smashing you like a dirt. So to dodge such an attack make sure you time well and roll on another side this should be well timed as you see him landing or a sec after his jump is complete. Don't worry if you get hit by it, perfect your moves and give another try later. After the damage to Laurence is done above 50% he will enter his next phase of the fight.
When you see Laurence has no legs left then you start with the Phase two of the fight and this doesn't mean he has weakened now or cannot attack anymore. Laurence can use his mouth to spit out Lava, but this can be spat within range so you can easily back off and avoid the attack. Immediately head back as you see Laurence is tilting his Head this means he is ready to spit the lava or you can perform you charged Visceral attack as he will be unable to move or dodge your attack at this movement.
In Phase Two he also has a unique attack where he raises his left arm and perform some kind of slice chops that provides you a massive damage. If not the Slice chops then he will definitely do 180 big swipes that may lead to direct Kill if you stand in front of him. The best thing to do is run away from him by roll sideways. At the last quarter of Laurence's health, he will start crawling around you(a bit scary).
To Avoid such an attack, you must directly head towards him and start charging wth maximum hits until his health is brought down to zero and when you see him getting charged just move away, let him attack and then back to the same strategy. Thus defeating the Boss Laurence in the DLC: The Old Hunter.