He beat the likes of Kevin De Bruyne, Marcus Rashford, Virgil van Dijk and Sadio Mane, to the award.
The captain played in 30 league matches until sustaining a knee injury this month that ruled him out of the final four games.
Henderson lifted the Premier League trophy at Anfield on Wednesday and becomes the third Liverpool player to win the FWA award in the space of seven years, following Luis Suárez in 2014 and Mohamed Salah in 2018.
The FWA Footballer of the Year is given to the player considered both to have had an outstanding impact on their club’s performance in the season, as well as having performed well individually throughout the campaign.
Henderson was one of five Liverpool players to receive votes, with Alisson, Virgil van Dijk, Trent Alexander-Arnold and Sadio Mane also picked by some journalists.
The Top 5
De Bruyne came second in the voting with Rashford third, while Alisson and Van Dijk rounded out the top five.
Upon receiving the award, Jordan Henderson told the FWA website;
“I’d like to say how appreciative I am of the support of those who voted for me and the Football Writers’ Association in general. You only have to look at the past winners of it, a number of whom I’ve been blessed to play with here at Liverpool, like Stevie (Gerrard), Luis (Suarez) and Mo (Salah) to know how prestigious it is.
“As grateful as I am I don’t feel like I can accept this on my own. I don’t feel like anything I’ve achieved this season or in fact during my whole career has been done on my own. I owe a lot to so many different people, but none more so than my current team-mates, who have just been incredible and deserve this every bit as much as I do.
“We’ve only achieved what we’ve achieved because every single member of our squad has been brilliant. Not just in matches, not just in producing the moments that make the headlines and the back pages, but every day in training.
“The players who’ve started the most games for us this season have been as good as they have been because of our culture and our environment at Melwood. No one individual is responsible for that – it’s a collective effort and that’s how I view accepting this honour.
“I accept it on behalf of this whole squad, because without them I’m not in a position to be receiving this honour. These lads have made me a better player – a better leader and a better person. If anything I hope those who voted for me did so partly to recognise the entire team’s contribution.
“Individual awards are nice and they are special and I will cherish this one, but an individual award without the collective achievement wouldn’t mean anywhere as much to me – if anything at all.”