From what I understand HP Lovecraft's grandfather was very wealthy and even a prominent Member of Parliament.

Howard Phillips Lovecraft's maternal grandfather was Whipple Van Buren Phillips, a prominent local businessman in Rhode Island, notably running the Owyhee Land and Irrigation Company, and for most of his early life Lovecraft and his mother Sarah Susan Phillips Lovecraft lived in his house, which included a stable for horses and servants. Whipple Phillips served in the Rhode Island House of Representatives for the 1870-1872 term.

Winfield Scott Lovecraft, the father of Howard, was a "commercial traveler" (read: traveling sales representative) for the Gorham Silver Company. In 1893 when Howard was three years old, the elder Lovecraft was committed to Butler Hospital; he died there five years later, probably of tertiary syphilis. Howard Lovecraft and his mother were then dependent upon Whipple Phillips for financial support.

In 1900, Phillips took a substantial financial hit when a dam built by his company failed, as did a subsequent one. In 1904, Phillips died, and his much-reduced estate was divided among his surviving children. To economize, Howard Lovecraft's boyhood home was sold off, and he and his mother moved into smaller quarters. The assets available were subsequently diminished when Susan Lovecraft invested some of it in her brother's business, which then failed.

So the family of two was living off a fixed sum (with a very small income from a mortgage on a local quarry which they had also inherited). Lovecraft was initially taught by private tutors, but after his grandfather's death began attendance at public schools. His attendance was irregular, marked by periods where he was withdrawn from school, and including a "nervous breakdown" or other ailment in 1908 which prevented him from graduating.

At this point in his life, Lovecraft should have graduated high school and gone on to the local university, or perhaps applied for West Point or gotten a job - but he did not. While not exactly idle during this period - there are indications he attended adult education classes and took a correspondence course in chemistry - he didn't do much to prepare for entering the workplace, although he did begin to pick up a bit of money revising the writings of others.

Lovecraft came to the attention of amateur journalism in 1914, and was soon prominent in the national level organizations. Money was a constant concern, but Lovecraft was at that point in his mid-late 20s with little formal education, no work experience, and unable to simply look for work. In 1917 Lovecraft did attempt to enlist in the Rhode Island National Guard, with an aim to serving in the war overseas, and was briefly accepted; however, his mother prevailed on the family physician to intervene, and Lovecraft's enlistment was rejected. The concerns of money are thought to have been a mental strain on his mother, who suffered a breakdown and was committed to Butler Hospital in 1919; she died there after a gallbadder surgery in 1921.

Shortly after his mother's death, Lovecraft met, through amateur journalism, Sonia Haft Greene, a White Russian emigre, and they began what turned out to be a courtship through letters. Greene was a highly successful milliner in New York City, and Lovecraft had been making slight inroads in selling his fiction - which expanded considerably in 1923, when Weird Tales hit the stands, and Lovecraft himself was welcomed by the editor (J. C. Henneberger) and readers of the pulp magazine with acclaim.

In 1924, Lovecraft and Sonia basically eloped to New York; he didn't tell his aunts about the marriage until three days after the wedding. At the time, they had certain prospects: Lovecraft's fiction was selling, Sonia had a high-paying position and five-figure savings, and he still had his revisory work - but shortly after the move, things began to go downhill. Sonia lost her job, possibly a chunk of her savings in a business venture, and began to suffer serious health issues; Henneberger, who had at one point offered Lovecraft the editorship of Weird Tales, lost the magazine, and the new editor Farnsworth Wright was more liable to reject Lovecraft's stories.

Lovecraft's letters from the period show that he did try to get a normal job during that period - sending out over a hundred letters, answering ads, etc. He did briefly find some work - stuffing envelopes, once, and he tried his hand as a salesman - but he lacked the commercial knack for the latter. Friends like Harry Houdini recommended him, but literary positions likewise simply didn't appear. Efforts to collect and publish his fiction met with failure. Living mostly off Sonia's savings, the Lovecrafts were forced to economize, even sell furniture.

Part of this, it should be understood, was Lovecraft's own peculiarities - he had no commercial drive whatsoever, no experience being employed, often had trouble keeping regular hours, and was largely unwilling to either relocate or accept menial work...the fact is that Lovecraft had basically not been prepared to take any sort of regular employment, and in his 30s found himself poorly equipped to do so, a fact which he would lament for basically the rest of his life.

In 1925, Sonia Lovecraft took a job out west; Lovecraft remained in Brooklyn, his furniture crammed into a smaller apartment. While he continued to do revisory work and some original fiction, he was largely supported by money sent by his wife and his aunts to make rent and see to his basic needs. In 1926, his apartment was broken into and he was robbed of all of his clothes, except what he was wearing. His aunts had him come home to Providence. The marriage with Sonia did not long survive; according to her account, the aunts could not permit the loss in social standing if it were seen that Howard's wife was working to support him.

For the rest of Lovecraft's life, he basically lived off of the dwindling inheritance from his parents and grandparents; living with his aunts to save money, working to revise the writings for others (who sometimes failed to pay), occasionally managing to sell his own fiction. He practiced tremendous economies, which with the aid of his friends enabled him to take advantage of low bus and train fares during the Great Depression to travel the country - east as far as New Orleans, south as far as Key West, north to Quebec - often eating only a single meal a day, even if that was only a donut and coffee. Fresh fruits and meat were largely unavailable at his price range, with Lovecraft preferring canned goods, becoming an especial connoisseur of canned beans. This is thought to have helped lead to his terminal illness.

Lovecraft's approach to writing fiction was essentially that of an auteur; while it was entirely possible to make good money writing for the pulps, it required writing quickly, in volume, and to the tastes and needs of the market - things which Lovecraft was loathe to do, as he decried creative and aesthetic sacrifices to the market (although he was willing to bend for ghostwritten works). Efforts to collect and publish his fiction during his lifetime largely failed; the two major efforts (The Shunned House in 1928 and The Shadow over Innsmouth in 1936) were both failures, and major publishing houses turned Lovecraft down repeatedly (in part, perhaps, because of Lovecraft's recalcitrance to submit). He earned a little from anthology reprints, but this was far before the point in time where that could really earn him enough to live on. Further, Weird Tales was almost his sole market, and Farnsworth Wright would often reject Lovecraft's best work for various real or perceived reasons. The rejections hurt Lovecraft's confidence, which slowed down his production of fiction even more.

He was clearly intellectual and that should have earned him good money.

It's worth pointing out that being intelligent or creative doesn't automatically equal making a good living. For comparison, the other two most notable writers at Weird Tales - Clark Ashton Smith and Robert E. Howard - were both also very ill-fitted to conventional employment. Howard's father was a country doctor in Texas, and Howard himself managed to graduate high school, but detested being employed by someone else, and set down to make his living as a pulp writer - which he did, by in many ways eschewing the principles that Lovecraft held to and writing in quantity and with speed, trying to match what editors were looking for - although he rarely sacrificed quality. Clark Ashton Smith was born of poor parents, never finished school, and was largely an autodidact; his teenage fame as a poet never translated into mainstream success, and like Howard and Lovecraft he couldn't stand regular employment - his friend George Sterling got a few rich folks to send him a stipend, but never enough to get out of poverty, and Smith earned most of his money as a day laborer, chopping wood and picking fruit, with his publishing ventures being largely expensive fiascoes.

Also, how meritous was he as a scientist? Was the quality of his science poor that made him earn less?

Lovecraft had a great interest in science from a very young age, but he didn't have the education to be a scientist, and math in particular was his bane in school - Lovecraft's biographer S. T. Joshi once speculated that it was Lovecraft's realization he would never be good enough at math to be an astronomer which set off his mental breakdown that didn't permit him to complete high school. Lovecraft's "scientific" writings are mostly restricted to juvenalia and a number of articles on astronomy for local newspapers; at one point Lovecraft and his friend C. M. Eddy, Jr. were commissioned to write an anti-occult work to be titled The Cancer of Superstition, but the project was never completed due to to Houdini's death in 1926.