Cruise missile submarine Severodvinsk was tracked on 16 July while the warship picked up attack submarine Vepr on 19 July, the Royal Navy has confirmed.
It's believed that the two Russian submarines were intercepted while heading for St Petersburg to take part in Russia's navy day celebrations due to be held on 31 July.
Other Nato forces continued to track the Russian subs as they sailed into the Baltic Sea towards their destination.
It's at least a smoother encounter than in 2020 when the Royal Navy's HMS Northumberland collided with a Russian submarine while filming for Channel 5 documentary Warship: Life At Sea.
Footage of the collision was later released, which caused damage to the Royal Navy vessel's sonar equipment and was not thought to be deliberate.
According to the Royal Navy, HMS Portland recently participated in a large-scale Nato's submarine hunting exercise involving a force of 11 ships, seven helicopters and 16 maritime patrol aircraft.
Commander Tim Leeder, HMS Portland's commanding officer, said the training had helped prepare the ship's crew for the real thing.
He said: "Our success on operations marks the culmination of many months of specialist training and exercises.
"Critically, the cohesiveness of Royal Navy, RAF and our allies capabilities ensures that we are capable of conducting and sustaining these types of anti-submarine operations in the North Atlantic."
"It is testament to my sailors’ dedication and professionalism, alongside that of our allies, that we are able to conduct this strategically crucial role."
Equipped with sonar, sensors, torpedoes and depth charges, the HMS Portland is well suited to hunting down and destroying submarines should it ever come to that.
This encounter comes as Royal Navy sailors are currently training Ukrainian personnel in their continuing efforts to repel Russia's invasion.
British sailors are teaching Ukrainian crews how to operate a pair of Sandown class minehunters which will be then sold to Ukraine to sweep the Black Sea for mines which could threaten shipping.
Russia and Ukraine recently agreed a deal which will allow ships to transport millions of tons worth of grain out of the war-torn country.
The Russian blockade imposed since the invasion has significantly harmed the world's food supply, triggering a rise in prices and shortages in some countries.
The ships will be searched in Turkish ports in an attempt to allay Russian fears that this naval corridor could open up a new avenue of weapons being sent into Ukraine.Featured Image Credit: Ministry of Defence / British Embassy Oslo/Twitter