“Notwithstanding” is a preposition. In Spanish, similar words or phrases are “a pesar de” or “no obstante”.
Some examples to help you:
• Notwithstanding the bad weather (a pesar del mal tiempo…) we went for a long walk in the forest.
• Notwithstanding the difficulties (a pesar de las dificultades…), I passed the Cambridge Advanced English exam.
• The political party in Spain, “PP”, has done well this year. Notwithstanding (no obstante), it is going to have a difficult task to win the next election.